Counting Occurrences of a String in an Array

ruby-talk
1

Hi,

I'm pretty new to Ruby, and I've been trying to figure out the best
way to do this with little luck.

I have an array that is all strings, and I need to count, for each
string in the array, how many times some substring appears in it.

So, for example, my array is ["aaa", "aab", "abb", "bbb"] and I want
to return a new array that tells me how many times "a" appears: [3, 2,
1, 0]

Can anyone point me in the right direction with this?

Thanks!

2

unknown wrote:

Hi,

I'm pretty new to Ruby, and I've been trying to figure out the best
way to do this with little luck.

I have an array that is all strings, and I need to count, for each
string in the array, how many times some substring appears in it.

So, for example, my array is ["aaa", "aab", "abb", "bbb"] and I want
to return a new array that tells me how many times "a" appears: [3, 2,
1, 0]

Can anyone point me in the right direction with this?

Thanks!

Sounds like greping !

["aaa", "aab", "abb", "bbb"].grep ....half of the answer.

···

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Posted via http://www.ruby-forum.com/\.

3

Hi --

···

On Wed, 11 Feb 2009, shrouded.shoyu@gmail.com wrote:

Hi,

I'm pretty new to Ruby, and I've been trying to figure out the best
way to do this with little luck.

I have an array that is all strings, and I need to count, for each
string in the array, how many times some substring appears in it.

So, for example, my array is ["aaa", "aab", "abb", "bbb"] and I want
to return a new array that tells me how many times "a" appears: [3, 2,
1, 0]

Can anyone point me in the right direction with this?

array.map {|str| str.count('a') }

David

--
David A. Black / Ruby Power and Light, LLC
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Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2\)

http://www.wishsight.com => Independent, social wishlist management!

4

So, for example, my array is ["aaa", "aab", "abb", "bbb"] and I want
to return a new array that tells me how many times "a" appears: [3, 2,
1, 0]

When you need to map elements of an array to another array, the method
to use is, no surprise here, map (a/k/a collect).

Now, finding the number occurences of a string inside another one can be
done in a few ways, depending on what you mean exactly. Scan is one :

[ "aaa", "aab", "abb", "bbb" ].map { |x| x.scan(/a/).length }

=> [3, 2, 1, 0]

Fred

···

Le 10 février 2009 à 22:51, shrouded.shoyu@gmail.com a écrit :
--
Perl already has _bless_, and we know what it does... [it] should also
have _smite_, and we know what it should do, too. If more languages had
_smite_ implemented, the remaining programmers would be better than the
current average. (Mike Andrews in the SDM)

5

Looks like a job for collect:

irb(main):008:0> a = ["aaa", "aab", "abb", "bbb"]
=> ["aaa", "aab", "abb", "bbb"]
irb(main):009:0> a.collect {|v| v.scan(/a/).size}
=> [3, 2, 1, 0]

···

shrouded.shoyu@gmail.com wrote:

Hi,

I'm pretty new to Ruby, and I've been trying to figure out the best
way to do this with little luck.

I have an array that is all strings, and I need to count, for each
string in the array, how many times some substring appears in it.

So, for example, my array is ["aaa", "aab", "abb", "bbb"] and I want
to return a new array that tells me how many times "a" appears: [3, 2,
1, 0]

Can anyone point me in the right direction with this?

Thanks!

--
RMagick: http://rmagick.rubyforge.org/