Class Arrays
- java.lang.Object
-
- uk.ac.starlink.ttools.func.Arrays
-
public class Arrays extends java.lang.Object
Functions which operate on array-valued cells. The array parameters of these functions can only be used on values which are already arrays (usually, numeric arrays). In most cases that means on values in table columns which are declared as array-valued. FITS and VOTable tables can have columns which contain array values, but other formats such as CSV cannot.If you want to calculate aggregating functions like sum, min, max etc on multiple values which are not part of an array, it's easier to use the functions from the
Lists
class.Note that none of these functions will calculate statistical functions over a whole column of a table.
The functions fall into a number of categories:
- Aggregating operations, which map an array value to a scalar, including
size
,count
,countTrue
,maximum
,minimum
,sum
,mean
,median
,quantile
,stdev
,variance
,join
. - Operations on one or more arrays which produce array results, including
add
,subtract
,multiply
,divide
,reciprocal
,condition
,slice
,pick
. Mostly these work on any numeric array type and return floating point (double precision) values, but some of them (slice
,pick
) have variants for different array types. - The function
array
, which lets you assemble a floating point array value from a list of scalar numbers. There are variants (intArray
,stringArray
) for some different array types.
- Since:
- 14 Jul 2008
- Author:
- Mark Taylor
- Aggregating operations, which map an array value to a scalar, including
-
-
Field Summary
Fields Modifier and Type Field Description static java.lang.String
ARRAY_ELEMENT_VARNAME
Array element variable name in arrayFunc expressions.static java.lang.String
ARRAY_INDEX_VARNAME
Array index variable name in arrayFunc expressions.
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Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description static double[]
add(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of adding either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.static double[]
array(double... values)
Returns a floating point numeric array built from the given arguments.static double[]
arrayFunc(java.lang.String expr, java.lang.Object inArray)
Returns a floating-point array resulting from applying a given function expression element-by-element to an input array.static double[]
condition(boolean[] flagArray, double trueValue, double falseValue)
Maps a boolean array to a numeric array by using supplied numeric values to represent true and false values from the input array.static byte[]
constant(int n, byte value)
static double[]
constant(int n, double value)
Returns a fixed-size array filled with a given constant value.static float[]
constant(int n, float value)
static int[]
constant(int n, int value)
static long[]
constant(int n, long value)
static short[]
constant(int n, short value)
static int
count(java.lang.Object array)
Returns the number of non-blank elements in the array.static int
countTrue(boolean[] array)
Returns the number of true elements in an array of boolean values.static double[]
divide(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of dividing either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.static double
dotProduct(java.lang.Object array1, java.lang.Object array2)
Returns the dot (scalar) product of two numeric arrays.static int
indexOf(double[] array, double item)
static int
indexOf(float[] array, double item)
static int
indexOf(int[] array, int item)
static int
indexOf(long[] array, long item)
static int
indexOf(short[] array, int item)
static int
indexOf(java.lang.Object[] array, java.lang.Object item)
Returns the position in a supplied array at which a given item appears.static int[]
intArray(int... values)
Returns an integer numeric array built from the given arguments.static int[]
intArrayFunc(java.lang.String expr, java.lang.Object inArray)
Returns an integer array resulting from applying a given function expression element-by-element to an input array.static java.lang.String
join(java.lang.Object array, java.lang.String joiner)
Returns a string composed of concatenating all the elements of an array, separated by a joiner string.static double
maximum(java.lang.Object array)
Returns the largest of the non-blank elements in the array.static double
mean(java.lang.Object array)
Returns the mean of all the non-blank elements in the array.static double
median(java.lang.Object array)
Returns the median of the non-blank elements in the array.static double
minimum(java.lang.Object array)
Returns the smallest of the non-blank elements in the array.static double[]
multiply(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of multiplying either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.static byte[]
pick(byte[] array, int... indices)
static double[]
pick(double[] array, int... indices)
Returns a selection of elements from a given array.static float[]
pick(float[] array, int... indices)
static int[]
pick(int[] array, int... indices)
static long[]
pick(long[] array, int... indices)
static short[]
pick(short[] array, int... indices)
static java.lang.Object[]
pick(java.lang.Object[] array, int... indices)
static java.lang.String[]
pick(java.lang.String[] array, int... indices)
static double
quantile(java.lang.Object array, double quant)
Returns a quantile value of the non-blank elements in the array.static double[]
reciprocal(java.lang.Object array)
Returns the result of taking the reciprocal of every element of a numeric array.static int[]
sequence(int n)
Returns an integer array of a given length with the values 0, 1, 2, ....static int
size(java.lang.Object array)
Returns the number of elements in the array.static byte[]
slice(byte[] array, int i0, int i1)
static double[]
slice(double[] array, int i0, int i1)
Returns a sub-sequence of values from a given array.static float[]
slice(float[] array, int i0, int i1)
static int[]
slice(int[] array, int i0, int i1)
static long[]
slice(long[] array, int i0, int i1)
static short[]
slice(short[] array, int i0, int i1)
static java.lang.Object[]
slice(java.lang.Object[] array, int i0, int i1)
static java.lang.String[]
slice(java.lang.String[] array, int i0, int i1)
static double
stdev(java.lang.Object array)
Returns the population standard deviation of all the non-blank elements in the array.static java.lang.String[]
stringArray(java.lang.String... values)
Returns a String array built from the given arguments.static double[]
subtract(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of subtracting either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.static double
sum(java.lang.Object array)
Returns the sum of all the non-blank elements in the array.static java.lang.Object
untypedArrayFunc(java.lang.String expr, java.lang.Object inArray)
Returns an untyped array resulting from applying a given function expression element-by-element to an input array.static double
variance(java.lang.Object array)
Returns the population variance of all the non-blank elements in the array.
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Field Detail
-
ARRAY_ELEMENT_VARNAME
@HideDoc public static final java.lang.String ARRAY_ELEMENT_VARNAME
Array element variable name in arrayFunc expressions.- See Also:
- Constant Field Values
-
ARRAY_INDEX_VARNAME
@HideDoc public static final java.lang.String ARRAY_INDEX_VARNAME
Array index variable name in arrayFunc expressions.- See Also:
- Constant Field Values
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Method Detail
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sum
public static double sum(java.lang.Object array)
Returns the sum of all the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- sum of all the numeric values in
array
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mean
public static double mean(java.lang.Object array)
Returns the mean of all the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- mean of all the numeric values in
array
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variance
public static double variance(java.lang.Object array)
Returns the population variance of all the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- variance of the numeric values in
array
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stdev
public static double stdev(java.lang.Object array)
Returns the population standard deviation of all the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- standard deviation of the numeric values in
array
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minimum
public static double minimum(java.lang.Object array)
Returns the smallest of the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- minimum of the numeric values in
array
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maximum
public static double maximum(java.lang.Object array)
Returns the largest of the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- maximum of the numeric values in
array
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median
public static double median(java.lang.Object array)
Returns the median of the non-blank elements in the array. Ifarray
is not a numeric array,null
is returned.- Parameters:
array
- array of numbers- Returns:
- median of the numeric values in
array
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quantile
public static double quantile(java.lang.Object array, double quant)
Returns a quantile value of the non-blank elements in the array. Which quantile is determined by thequant
value; values of 0, 0.5 and 1 give the minimum, median and maximum respectively. A value of 0.99 would give the 99th percentile.- Parameters:
array
- array of numbersquant
- number in the range 0-1 deterining which quantile to calculate- Returns:
- quantile corresponding to
quant
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size
public static int size(java.lang.Object array)
Returns the number of elements in the array. Ifarray
is not an array, zero is returned.- Parameters:
array
- array- Returns:
- size of
array
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count
public static int count(java.lang.Object array)
Returns the number of non-blank elements in the array. Ifarray
is not an array, zero is returned.- Parameters:
array
- array (may or may not be numeric)- Returns:
- number of non-blank elements in
array
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countTrue
public static int countTrue(boolean[] array)
Returns the number of true elements in an array of boolean values.- Parameters:
array
- array of true/false values- Returns:
- number of true values in
array
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join
public static java.lang.String join(java.lang.Object array, java.lang.String joiner)
Returns a string composed of concatenating all the elements of an array, separated by a joiner string. Ifarray
is not an array, null is returned.- Parameters:
array
- array of numbers or stringsjoiner
- text string to interpose between adjacent elements- Returns:
- string composed of
array
elements separated byjoiner
strings - Examples:
join(array(1.5,2.1,-3.9), "; ") = "1.5; 2.1; -3.9"
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dotProduct
public static double dotProduct(java.lang.Object array1, java.lang.Object array2)
Returns the dot (scalar) product of two numeric arrays. If either argument is not an array, or if the arrays are not of the same length, a blank value is returned.- Parameters:
array1
- first arrayarray2
- second array- Returns:
- sum of element-wise products of input arrays
- Examples:
dotProduct(array(3,4,5), array(1,2,3)) = 26
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add
public static double[] add(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of adding either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.If the arguments are not as expected (e.g. arrays of different lengths, both scalars, not numeric) then null is returned.
- Parameters:
arrayOrScalar1
- first numeric array/scalararrayOrScalar2
- second numeric array/scalar- Returns:
- element-by-element result of
arrayOrScalar1 + arrayOrScalar2
, the same length as the input array(s) - Examples:
add(array(1,2,3), array(0.1,0.2,0.3)) = [1.1, 2.2, 3.3]
,add(array(1,2,3), 10) = [11,12,13]
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subtract
public static double[] subtract(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of subtracting either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.If the arguments are not as expected (e.g. arrays of different lengths, both scalars, not numeric) then null is returned.
- Parameters:
arrayOrScalar1
- first numeric array/scalararrayOrScalar2
- second numeric array/scalar- Returns:
- element-by-element result of
arrayOrScalar1 - arrayOrScalar2
, the same length as the input array(s) - Examples:
subtract(array(1,2,3), array(0.1,0.2,0.3)) = [0.9, 1.8, 2.7]
,subtract(array(1,2,3), 1.0) = [0, 1, 2]
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multiply
public static double[] multiply(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of multiplying either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.If the arguments are not as expected (e.g. arrays of different lengths, both scalars, not numeric) then null is returned.
- Parameters:
arrayOrScalar1
- first numeric array/scalararrayOrScalar2
- second numeric array/scalar- Returns:
- element-by-element result of
arrayOrScalar1 * arrayOrScalar2
, the same length as the input array(s) - Examples:
multiply(array(1,2,3), array(2,4,6)) = [2, 8, 18]
,multiply(2, array(1,2,3)) = [2, 4, 6]
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divide
public static double[] divide(java.lang.Object arrayOrScalar1, java.lang.Object arrayOrScalar2)
Returns the element-by-element result of dividing either two numeric arrays of the same length, or an array and a scalar considered as if an array of the right length.If the arguments are not as expected (e.g. arrays of different lengths, both scalars, not numeric) then null is returned.
- Parameters:
arrayOrScalar1
- first numeric array/scalararrayOrScalar2
- second numeric array/scalar- Returns:
- element-by-element result of
arrayOrScalar1 / arrayOrScalar2
, the same length as the input array(s) - Examples:
divide(array(0,9,4), array(1,3,8)) = [0, 3, 0.5]
,divide(array(50,60,70), 10) = [5, 6, 7]
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reciprocal
public static double[] reciprocal(java.lang.Object array)
Returns the result of taking the reciprocal of every element of a numeric array. If the suppliedarray
argument is not a numeric array,null
is returned.- Parameters:
array
- array input- Returns:
- array output,
the same length as the
array
parameter - Examples:
reciprocal(array(1,2,0.25) = [1, 0.5, 4]
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condition
public static double[] condition(boolean[] flagArray, double trueValue, double falseValue)
Maps a boolean array to a numeric array by using supplied numeric values to represent true and false values from the input array.This has the same effect as applying the expression
outArray[i] = flagArray[i] ? trueValue : falseValue
.- Parameters:
flagArray
- array of boolean valuestrueValue
- output value corresponding to an input true valuefalseValue
- output value corresponding to an input false value- Returns:
- output numeric array, same length as
flagArray
- Examples:
condition([true, false, true], 1, 0) = [1, 0, 1]
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constant
public static double[] constant(int n, double value)
Returns a fixed-size array filled with a given constant value.Note: This documents the double-precision version of the routine. Corresponding routines exist for other data types (
float
,long
,int
,short
,byte
).- Parameters:
n
- size of output arrayvalue
- value of every element in the output array- Returns:
n
-element array with every element set tovalue
- Examples:
constant(5, 23.5) = [23.5, 23.5, 23.5, 23.5, 23.5]
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constant
@HideDoc public static float[] constant(int n, float value)
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constant
@HideDoc public static byte[] constant(int n, byte value)
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constant
@HideDoc public static short[] constant(int n, short value)
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constant
@HideDoc public static int[] constant(int n, int value)
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constant
@HideDoc public static long[] constant(int n, long value)
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slice
public static double[] slice(double[] array, int i0, int i1)
Returns a sub-sequence of values from a given array.The semantics are like python array slicing, though both limits have to be specified: the output array contains the sequence of elements in the input array from
i0
(inclusive) toi1
(exclusive). If a negative value is given in either case, it is added to the length of the input array, so that -1 indicates the last element of the input array. The indices are capped at 0 and the input array length respectively, so a large positive value may be used to indicate the end of the array. If the end index is less than or equal to the start index, a zero-length array is returned.Note: This documents the double-precision version of the routine. Corresponding routines exist for other data types (
float
,long
,int
,short
,byte
,String
,Object
).- Parameters:
array
- input arrayi0
- index of first element, inclusive (may be negative to count back from the end)i1
- index of the last element, exclusive (may be negative to count back from the end)- Returns:
- array giving the sequence of
elements specified by
i0
andi1
- Examples:
slice(array(10,11,12,13), 0, 3) = [10, 11, 12]
,slice(array(10,11,12,13), -2, 999) = [12, 13]
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slice
@HideDoc public static float[] slice(float[] array, int i0, int i1)
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slice
@HideDoc public static long[] slice(long[] array, int i0, int i1)
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slice
@HideDoc public static int[] slice(int[] array, int i0, int i1)
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slice
@HideDoc public static short[] slice(short[] array, int i0, int i1)
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slice
@HideDoc public static byte[] slice(byte[] array, int i0, int i1)
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slice
@HideDoc public static java.lang.String[] slice(java.lang.String[] array, int i0, int i1)
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slice
@HideDoc public static java.lang.Object[] slice(java.lang.Object[] array, int i0, int i1)
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pick
public static double[] pick(double[] array, int... indices)
Returns a selection of elements from a given array.The output array consists of one element selected from the input array for each of the supplied index values. If a negative value is supplied for an index value, it is added to the input array length, so that -1 indicates the last element of the input array. If the input array is null, null is returned. If any of the index values is out of the range of the extent of the input array, an error results.
Note: This documents the double-precision version of the routine. Corresponding routines exist for other data types (
float
,long
,int
,short
,byte
,String
,Object
).- Parameters:
array
- input arrayindices
- one or more index into the input array (may be negative to count back from the end)- Returns:
- array giving the elements specified by
indices
- Examples:
pick(array(10,11,12,13), 0, 3) = [10, 13]
,pick(array(10,11,12,13), -1, -2, -3) = [13, 12, 11]
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pick
@HideDoc public static float[] pick(float[] array, int... indices)
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pick
@HideDoc public static long[] pick(long[] array, int... indices)
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pick
@HideDoc public static int[] pick(int[] array, int... indices)
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pick
@HideDoc public static short[] pick(short[] array, int... indices)
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pick
@HideDoc public static byte[] pick(byte[] array, int... indices)
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pick
@HideDoc public static java.lang.String[] pick(java.lang.String[] array, int... indices)
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pick
@HideDoc public static java.lang.Object[] pick(java.lang.Object[] array, int... indices)
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arrayFunc
public static double[] arrayFunc(java.lang.String expr, java.lang.Object inArray)
Returns a floating-point array resulting from applying a given function expression element-by-element to an input array. The output array is the same length as the input array.The supplied expression can use the variable "
x
" to refer to the corresponding element of the input array, and "i
" to refer to its (zero-based) index. The various functions and operators from the expression language can all be used, but it is currently not possible to reference other table column values.If there is an error in the expression, a blank value (not an array) will be returned.
- Parameters:
expr
- expression mapping input to output array valuesinArray
- input array- Returns:
- floating point array with the same number of elements as
inArray
, or null for a badexpr
- Examples:
arrayFunc("3*x",array(0,1,2,3,NaN)) = [0, 3, 6, 9, NaN]
,arrayFunc("pow(2,i)+x", array(0.5,0.5,0.5,0.5)) = [1.5, 2.5, 4.5, 8.5]
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intArrayFunc
public static int[] intArrayFunc(java.lang.String expr, java.lang.Object inArray)
Returns an integer array resulting from applying a given function expression element-by-element to an input array. The output array is the same length as the input array.The supplied expression can use the variable "
x
" to refer to the corresponding element of the input array, and "i
" to refer to its (zero-based) index. The various functions and operators from the expression language can all be used, but it is currently not possible to reference other table column values.If there is an error in the expression, a blank value (not an array) will be returned.
- Parameters:
expr
- expression mapping input to output array valuesinArray
- input array- Returns:
- floating point array with the same number of elements as
inArray
, or null for a badexpr
- Examples:
intArrayFunc("-x",sequence(5)) = [0, -1, -2, -3, -4]
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untypedArrayFunc
@HideDoc public static java.lang.Object untypedArrayFunc(java.lang.String expr, java.lang.Object inArray)
Returns an untyped array resulting from applying a given function expression element-by-element to an input array. The runtime type of the output value is determined by the compiled type of the supplied expression, but since this method only has type Object, it has to be cast manually to the actual type before anything much can be done with it. For that reason it's not publicised in the user documentation.- Parameters:
expr
- expression mapping input to output array valuesinArray
- input array- Returns:
- untyped array with the same number of elements as
inArray
, or null for a badexpr
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indexOf
public static int indexOf(java.lang.Object[] array, java.lang.Object item)
Returns the position in a supplied array at which a given item appears. The result is zero-based, so if the supplieditem
is the first entry in thearray
, the return value will be zero.If the item does not appear in the array, -1 is returned. If it appears multiple times, the index of its first appearance is returned.
If
indexOf(array, item)==n
, thenarray[n]
is equal toitem
.Note: This documents the
Object
version of the routine. Corresponding routines exist for other data types (double
,float
,long
,int
,short
).- Parameters:
array
- array which may contain the supplied itemitem
- entry to look for in the array- Returns:
- the index of
item
inarray
, or -1 - Examples:
indexOf(stringArray("QSO", "BCG", "SNR"), "BCG") = 1
,indexOf(stringArray("QSO", "BCG", "SNR"), "TLA") = -1
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indexOf
@HideDoc public static int indexOf(double[] array, double item)
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indexOf
@HideDoc public static int indexOf(float[] array, double item)
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indexOf
@HideDoc public static int indexOf(long[] array, long item)
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indexOf
@HideDoc public static int indexOf(int[] array, int item)
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indexOf
@HideDoc public static int indexOf(short[] array, int item)
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sequence
public static int[] sequence(int n)
Returns an integer array of a given length with the values 0, 1, 2, ....- Parameters:
n
- length of array- Returns:
n
-element array, (0, 1, 2, ...n
-1)- Examples:
sequence(4) = (0, 1, 2, 3)
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array
public static double[] array(double... values)
Returns a floating point numeric array built from the given arguments.- Parameters:
values
- one or more array elements- Returns:
- array
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intArray
public static int[] intArray(int... values)
Returns an integer numeric array built from the given arguments.- Parameters:
values
- one or more array elements- Returns:
- array
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stringArray
public static java.lang.String[] stringArray(java.lang.String... values)
Returns a String array built from the given arguments.- Parameters:
values
- one or more array elements- Returns:
- array
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