3.2.1.0 table.calc

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table.calc - Function

3.2.1 !!!NOT IMPLEMENTED!!! Calculate an expression on a table
Description

!!!NOT IMPLEMENTED!!!

Get the result from the calculation of an expression on a table

The expression can be any expression that can be given in the WHERE clause of a SELECT expression (thus including subqueries). The given expression determines if the result is a scalar, a vector, or a record containing arrays. See the examples below.

Arguments


Inputs
expr	Expression string
	allowed:	string
	Default:

Returns
anyvariant

Example

!!!NOT IMPLEMENTED!!!

tb.open("3C273XC1.MS")
tb.calc (’DATA+1’)

returns a (potentially enormous) record where a field contains the value of the expression for the row with that number. Note that it returns a record because for each row the expression results in an array. It should be clear that this example is useless. However, something like this could be useful for a column with (very) small arrays.

tb.open("3C273XC1.MS")
tb.calc (’ntrue(FLAG)’)

returns for each row the number of flags set. The result is a vector, because for each row the expression results in a scalar.

tb.open("3C273XC1.MS")
tb.calc (’sum([select from $1 giving [ntrue(FLAG)]])’)

returns the total number of flags set in the table (in a single scalar). It is the same as

sum(tb.calc (’ntrue(FLAG)’))

The latter is easier to write, but sends (much) more data over the casapy bus.

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