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10.5.9 Arrays

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:

sum( array )
Returns the sum of all the non-blank elements in the array. If array is not a numeric array, null is returned.
mean( array )
Returns the mean of all the non-blank elements in the array. If array is not a numeric array, null is returned.
variance( array )
Returns the population variance of all the non-blank elements in the array. If array is not a numeric array, null is returned.
stdev( array )
Returns the population standard deviation of all the non-blank elements in the array. If array is not a numeric array, null is returned.
minimum( array )
Returns the smallest of the non-blank elements in the array. If array is not a numeric array, null is returned.
maximum( array )
Returns the largest of the non-blank elements in the array. If array is not a numeric array, null is returned.
median( array )
Returns the median of the non-blank elements in the array. If array is not a numeric array, null is returned.
quantile( array, quant )
Returns a quantile value of the non-blank elements in the array. Which quantile is determined by the quant 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.
size( array )
Returns the number of elements in the array. If array is not an array, zero is returned.
count( array )
Returns the number of non-blank elements in the array. If array is not an array, zero is returned.
countTrue( array )
Returns the number of true elements in an array of boolean values.
join( array, joiner )
Returns a string composed of concatenating all the elements of an array, separated by a joiner string. If array is not an array, null is returned.
add( array1, array2 )
Returns the result of adding two numeric arrays element by element. Both arrays must be numeric, and the arrays must have the same length. If either of those conditions is not true, null is returned. The types of the arrays do not need to be the same, so for example it is permitted to add an integer array to a floating point array.
add( array, constant )
Returns the result of adding a constant value to every element of a numeric array. If the supplied array argument is not a numeric array, null is returned.
subtract( array1, array2 )
Returns the result of subtracting one numeric array from the other element by element. Both arrays must be numeric, and the arrays must have the same length. If either of those conditions is not true, null is returned. The types of the arrays do not need to be the same, so for example it is permitted to subtract an integer array from a floating point array.
multiply( array1, array2 )
Returns the result of multiplying two numeric arrays element by element. Both arrays must be numeric, and the arrays must have the same length. If either of those conditions is not true, null is returned. The types of the arrays do not need to be the same, so for example it is permitted to multiply an integer array by a floating point array.
multiply( array, constant )
Returns the result of multiplying every element of a numeric array by a constant value. If the supplied array argument is not a numeric array, null is returned.
divide( array1, array2 )
Returns the result of dividing two numeric arrays element by element. Both arrays must be numeric, and the arrays must have the same length. If either of those conditions is not true, null is returned. The types of the arrays do not need to be the same, so for example it is permitted to divide an integer array by a floating point array.
reciprocal( array )
Returns the result of taking the reciprocal of every element of a numeric array. If the supplied array argument is not a numeric array, null is returned.
condition( flagArray, trueValue, 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.

array( values, ... )
Returns a floating point numeric array built from the given arguments.
intArray( values, ... )
Returns an integer numeric array built from the given arguments.
stringArray( values, ... )
Returns a String array built from the given arguments.


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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk