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table.calc - Function
3.2.1 TaQL expression with calc to calculate an expression on a table
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.
TaQL prefix for style and ordering etc ...check TaQL note 199 for usage
using style base0, endincl, fortranorder
Show the full taql command used
tb.calc(’[select from ngc5921.ms giving [mean(abs(DATA))]]’)
find the mean of the abs of each row of the DATA column of the MeasurementSet ngc5921.ms
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.calc(’[select from ngc5921.ms.contsub giving [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.calc(’sum([select from ngc5921.ms.contsub giving [ntrue(FLAG)]])’)
returns the total number of flags set in the table (in a single
using subrow array
tb.calc(’median([select from ngc5921.ms where ANTENNA1==3 && ANTENNA2==5 giving [abs(DATA[0,31])]])’)
The above will find the median channel 31 and 0th pol of the requested baseline formed with antennas 3 and 5.
Note that the that the default casa order of arrays is fortran order ...pol axis is before channel axis
tb.calc(’median([select from ngc5921.ms where ANTENNA1==3 && ANTENNA2==5 giving [abs(DATA[31, 0])]])’, prefix=’using style python’)
Now the same is as the above but using the python style of axis ordering access
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