Call a function multiple times and get a list of results

5.times.collect { f }

(Assuming no parameters. map is an alias to collect; I prefer the name collect when actually collecting as it seems more communicative, but YMMV.)

I also prefer the longer 5.times instead of (1..5). This seems more communicative: I'm not really "iterating over a range", I'm "doing something five times".

IMO the answer is slightly counter-intuitive in this case, since I'm not really running collect five times, but collect.5.times { f } doesn't work, so we play a bit of a mental game anyway.

Try the block form of the Array constructor if you want zero based increasing arguments:

Array.new(5) {|x| (x+1).to_f} # => [1.0, 2.0, 3.0, 4.0, 5.0]
Array.new(10) { rand } # => [0.794129655156092, ..., 0.794129655156092]

You could just shorten your code by not putting to_a ... (1..5) is an enumerable so it works with map.

(1..5).map!{f}