# Arrays, difference of operation

**URL:** <https://www.ruby-forum.com/t/arrays-difference-of-operation/147390>\
**Category:** Ruby\
**Created:** [September 1, 2008, 11:11am UTC](https://www.ruby-forum.com/t/arrays-difference-of-operation/147390 "2008-09-01T11:11:32Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Mayuresh\_K](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/839c29/32.png) [@Mayuresh\_K](https://www.ruby-forum.com/u/Mayuresh_K)\
**Post date:** [September 1, 2008, 11:11am UTC](https://www.ruby-forum.com/t/arrays-difference-of-operation/147390/1 "2008-09-01T11:11:32Z")

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Hello,

I tried the following;  
a = [3, 2, 1]  
followed by;  
a[3] = a[2] - 1  
then, a contained [3, 2, 1, 0]

but, if I did the following;  
b = “hello everybody”  
followed by;  
b[“body”] = “one”  
then, b contained “hello everyone”

I can understand that a is an array holding numbers and when I do a[3]  
it is performing an operation on element 4, while b is an array  
holding characters and when I do a b[“body”] it seeks out the part of  
that string containing “body” and does an operation on it.

So, to do an operation on 3 in array a, I tried doing a[“3”] = 4 which  
gave an error as expected.

I’m a bit confused about this whole array thing, could someone please  
elaborate on the above two different results for array operations?  
Also, how would I seek an element in a numeric array without referring  
to its index?

Best,

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<div class="post-metadata">

**Author:** ![Mayuresh\_K](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/839c29/32.png) [@Mayuresh\_K](https://www.ruby-forum.com/u/Mayuresh_K)\
**Post date:** [September 1, 2008, 11:20am UTC](https://www.ruby-forum.com/t/arrays-difference-of-operation/147390/2 "2008-09-01T11:20:01Z")

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Mayuresh K. wrote:

> I’m a bit confused about this whole array thing, could someone please  
> elaborate on the above two different results for array operations?  
> Also, how would I seek an element in a numeric array without referring  
> to its index?

Hello.

Your confussion comes from the fact that you assume that [] means an  
array. In Ruby, [] means whatever you want. If a is an array, then  
a[index] is an operation of reading the specified element, and  
a[index]=value is the operation of writing the element. They can also be  
written as a. and a.[]=(index,value), as [] and []= are just  
method names.

As these are methods, they can be defined differently for other classes  
than Array. For example, for String they are defined as “find the text  
(and replace it with the value)”. If you define your class, you can even  
do this:

class K  
def   
puts “#{a}:#{b}:#{c}”  
end  
end

K::new[2,:f,“asd”]

As you see, the result has nothing to do with arrays. It’s just a  
method, the difference is only the fact that you can use the short  
notation a[x] instead of a..

TPR.

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<div class="post-metadata">

**Author:** ![Mayuresh\_K](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/839c29/32.png) [@Mayuresh\_K](https://www.ruby-forum.com/u/Mayuresh_K)\
**Post date:** [September 1, 2008, 11:25am UTC](https://www.ruby-forum.com/t/arrays-difference-of-operation/147390/3 "2008-09-01T11:25:40Z")

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Mayuresh K. wrote:

> b = “hello everybody”  
> […]  
> b is an array holding characters

No, it’s not. [“a”, “b”, “c”] is an array containing characters. “hello  
everybody” is a string. String#[] has features that Array#[] does not.  
Which  
it can have for the very simple reason that those are two different  
methods  
in two entirely different classes.

> Also, how would I seek an element in a numeric array without referring  
> to its index?

Array#find

HTH,  
Sebastian