From: "David A. Black" <dblack@...>
Date: 2008-04-27T00:45:33+09:00
Subject: Re: All occurances of a  character in a string

Hi --

On Sun, 27 Apr 2008, Robert Klemme wrote:

> On 26.04.2008 16:53, David A. Black wrote:
>> Hi --
>> 
>> On Sat, 26 Apr 2008, Raghu Go wrote:
>> 
>>> Hi - I am trying to figure out the ruby way of printing all occurances
>>> of a character in a string..
>>> 
>>> The index method on string gives only the first occurance only.
>>> 
>>> Example input string - abbccdaab
>>> desired output - 'a' = 0 6 7
>>>                 'b' = 1 2 8
>>>                 'c' = 3 4
>>>                 'd' = 5
>>> 
>>> Any help greatly appreciated..
>> 
>> I have this really strong feeling that there's a really easy way, but
>> I can't think of it or find it. Meanwhile, if you're using 1.9 you
>> could do something like:
>>
>>    str = "abcdbcdae"
>>
>>    h = Hash.new {|h,k| h[k] = [] }
>>    str.each_char.map.with_index {|char, i| h[char] << i }
>> 
>> which would put a hash of results in h.
>
> In 1.8
>
> irb(main):001:0> require 'enumerator'
> => true
> irb(main):002:0> str = "abcdbcdae"
> => "abcdbcdae"
> irb(main):003:0> ind = Hash.new {|h,k| h[k]=[]}
> => {}
> irb(main):004:0> str.to_enum(:scan,/./).each_with_index {|c,i|ind[c]<<i}
> => #<Enumerable::Enumerator:0x7ff75768>
> irb(main):005:0> ind
> => {"a"=>[0, 7], "b"=>[1, 4], "c"=>[2, 5], "d"=>[3, 6], "e"=>[8]}
>
>> I just have this hunch that there was a way to accumulate offsets from
>> a scan or gsub operation, but I can't come up with it.
>
> Like this?
>
> irb(main):017:0> str = "abcdbcdae"
> => "abcdbcdae"
> irb(main):018:0> ind = Hash.new {|h,k| h[k]=[]}
> => {}
> irb(main):019:0> str.scan(/./) {|c| ind[c] << $`.length}
> => "abcdbcdae"
> irb(main):020:0> ind
> => {"a"=>[0, 7], "b"=>[1, 4], "c"=>[2, 5], "d"=>[3, 6], "e"=>[8]}

It may well have been that, or something like it.


David

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