Counting Occurrences of a String in an Array


#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.


#3

Hi –

On Wed, 11 Feb 2009, removed_email_address@domain.invalid wrote:

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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#4

removed_email_address@domain.invalid wrote:

1, 0]

Can anyone point me in the right direction with this?

Thanks!

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]


#5

Le 10 février 2009 à 22:51, removed_email_address@domain.invalid a écrit :

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