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kdb array map - how to apply a function to every element of an array?

How does one apply a function to every element of an array in kdb? For example, to square an array of numbers in various languages:

javascript: [1,2,3,4].map(square)          -> [1,4,9,16]
python:     [square(x) for x in [1,2,3,4]] -> [1,4,9,16]
kdb:        {[x] x*x} (1;2;3;4)            -> 1 4 9 16

So I thought I'd write another function that takes a date and returns the name of a CSV file for that date:

q)gobble:{[x] string[x-1970.01.01],".csv"}
q)gobble .z.d // .z.d == today
"16781.csv"

Hurrah. So now I should be able to apply that function to an array of dates and get an array of strings in response, thought I. Foolish mortal:

q)gobble .z.d + til 5 // .z.d + til 5 == array of 5 days starting today
"16781"
"16782"
"16783"
"16784"
"16785"
"."
"c"
"s"
"v"

Obviously squaring in kdb was a special case of some kind, not to be generalised to all functions. How can I tell KDB to apply an arbitrary function to each date in turn, pretty please? Many thanks!

Solution

  • See each 

    q)gobble each .z.d + til 5
   "16782.csv"
   "16783.csv"
   "16784.csv"
   "16785.csv"
   "16786.csv"

    The square operation worked as * can operate on atoms as well as lists

    q)1 2 3 4 * 1 2 3 4
   1 4 9 16