Saturday, May 07, 2016

kdb+/q - Running a function multiple times and concatenating results

Let's say that you have a q function that you want to run for multiple inputs (for example, a list of dates) and you want to concatenate the outputs of each function call into a single table. This is demonstrated below:

// A function that returns some data for a single date.
getData:{[dt]
    t:select from data where date=dt;
    // do some more stuff
    t}

// list of dates
dates:2016.01.01+til 10

// call the function for each date and join results
result:(uj/) getData each dates;

// or, if you want to do some processing after each function call:
result:(uj/) {[dt;param]
    t:getData[dt];
    // do some stuff with param
    t}[;`foo] each dates;

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