Multiply number within array using an iterator

Question

If I would create a new array out of a preexisting one and modify the content using math operators, what would be a good way to do so? When I try with the code below, I receive an error about undefined methods.

ary1 = [1, 2, 3, 4, 5]
ary2 = ary1.each { |i| 
    ary1[i] = ary1[i] * 10
}
p ary1
p ary2

I assume that math operators are not included in the Array class.

ruby has strange syntax for that, is that a lambda? Or a "proc" as I've heard they're called in ruby? this question likely fits better on StackOverflow as it's technically specific to how to do X in Ruby or moreover "Why doesn't this code work in Ruby" — Jimmy Hoffa
– Jimmy Hoffa, Commented Jan 3, 2013 at 14:17
"I assume that math operators are not included in the Array class.". Array has no need for math operators because it's a container of other objects. The objects themselves might have math operators. Array does have "set" operators, but those have a different purpose. Typically we use map and its aliases, or each_with_object or inject to manipulate/coerce the contents of an array. — the Tin Man
– the Tin Man, Commented Jan 3, 2013 at 16:41
*, +, - are the math operators for Array. This is easily checked by using ri or checking Array class on ruby-doc.org as seen here. The problem was that you were trying to use * on nil not on Array. — vgoff
– vgoff, Commented Jan 4, 2013 at 18:40

Andrew Haines · Accepted Answer · 2013-01-03 14:34:34Z

8

You're looking for the map function (docs):

ary1 = [1, 2, 3, 4, 5]
ary2 = ary1.map {|value| value * 10}

map is generally a great way to produce a new array by transforming a given array. You pass it a block, which is called for each item in the array. The block receives each item - not the index - as an argument, which I've called value. The return values of the block are collected into a new array, which is then returned when the map function completes.

edited Jan 3, 2013 at 14:34

answered Jan 3, 2013 at 14:22

Andrew Haines

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vgoff Over a year ago

The interesting thing is that the word 'collected' was used to describe the behavior for map and not surprisingly collect is an alias for map. ary1 = [*(1..5)] ary2 = ary1.collect {|value| value * 10} (Since the edit got rejected...)

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