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### B.1.8 Arrays

Functions which perform aggregating operations on array-valued cells. The functions in this class such as `mean`, `sum`, `maximum` etc can only be used on values which are already 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.

There is also a set of functions named `array` with various numbers of arguments, which let you assemble an array value from a list of scalar numbers. This can be used for instance to get the mean of a set of three magnitudes by using an expression like "`mean(array(jmag, hmag, kmag))`".

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.
array( x1 )
  Returns a numeric array built from a given element.
array( x1, x2 )
  Returns a numeric array built from given elements.
array( x1, x2, x3 )
  Returns a numeric array built from given elements.
array( x1, x2, x3, x4 )
  Returns a numeric array built from given elements.
array( x1, x2, x3, x4, x5 )
  Returns a numeric array built from given elements.
array( x1, x2, x3, x4, x5, x6 )
  Returns a numeric array built from given elements.
array( x1, x2, x3, x4, x5, x6, x7 )
  Returns a numeric array built from given elements.
array( x1, x2, x3, x4, x5, x6, x7, x8 )
  Returns a numeric array built from given elements.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@bristol.ac.uk