# Re: Sorting arrays

**URL:** <https://www.ruby-forum.com/t/re-sorting-arrays/96496>\
**Category:** Ruby\
**Created:** [June 29, 2006, 1:14am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496 "2006-06-29T01:14:30Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 1:14am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/1 "2006-06-29T01:14:30Z")

</div>

You can use the sort method on the entire Array:

sorted=[1, 2, “three”]  
unsorted=[6,5,‘four’]  
a = sorted+unsorted  
b = a.sort { |x,y| x.to\_s \<=\> y.to\_s}  
=\>b is then [1, 2, 5, 6, “four”, “three”] (that’s because ‘1’ was  
compared  
to ‘four’ etc.)

Best regards,

Axel

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 1:17am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/2 "2006-06-29T01:17:38Z")

</div>

Apologies, I can’t use array.sort. This is to build my own.

Stuart

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 1:54am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/3 "2006-06-29T01:54:36Z")

</div>

On 6/28/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Best regards,
> 
> Axel

Dark A. wrote:

> Apologies, I can’t use array.sort. This is to build my own.

This sounds like a homework problem…?

In either case, your description is a little fuzzy. The way you describe  
it doesn’t make sense. This usually means you haven’t fully grasped the  
problem. Before jumping into the programming, write out what you want to  
accomplish on paper and make certain you completely understand what you  
wish to do, and how you will go about it.

Then try to solve it programmatically. If you have trouble with that  
piece, come back to the list. That’s my advice.

Good luck!

-Justin

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 2:38am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/4 "2006-06-29T02:38:46Z")

</div>

Actually it’s from Chris P.'s book, Learning to Program. I thought  
it was a bit fuzzy in the book, not so much my understanding but the  
suggestions he makes to accomplish the task. His idea is to have two  
additional lists, or arrays , one called “already sorted”, and the  
other “unsorted”. I’m just being repetetive here to make the point of  
where his advice is fuzzy. It reads as if you would use the first  
array (where the strings were put) and test those against themselves  
to find the smallest one, where the smallest (one that returns true)  
goes into the sorted, repeat and the ones that return false go into  
unsorted. Then the next iteration , or final stage is testing the  
sorted list against the unsorted list.

Using “insertion sort” it seemed that things were moved around in just  
the initial array.

Stuart

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 4:22am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/5 "2006-06-29T04:22:12Z")

</div>

Dark A. wrote:

> sorted list against the unsorted list.
> 
> Using “insertion sort” it seemed that things were moved around in just  
> the initial array.
> 
> Stuart

Oh, okay, sorry for my misunderstanding! I didn’t pay attention to who  
had posted.  
That’s not really insertion sort, no…here’s one way to do it  
(warning: spoilers ahead):

#if you can use Array#min:

list = [“aword”, “cword”, “gword”, “zword”, “dword”, “qword”, “pword”]  
unsorted = []  
sorted = []

sorted \<\< list.min #add the smallest to sorted  
unsorted = list - sorted #add the rest to unsorted

until unsorted.empty? #when unsorted is empty, we are done  
sorted \<\< unsorted.min #put the smallest value into sorted  
unsorted.delete(unsorted.min) #take it out of unsorted  
end

p sorted #all sorted!

* * *

#if you can’t use Array#min:

list = [“aword”, “cword”, “gword”, “zword”, “dword”, “qword”, “pword”]  
unsorted = []  
sorted = []

unsorted = list.dup #make a copy of the list of words so we don’t  
destroy the original!

until unsorted.empty? #when unsorted is empty, we are done

```
min = unsorted[0] #get our initial 'minimum value'

unsorted.each do |word|
   if word < min #check the rest of the values

```

against it  
min = word #if we find something smaller,  
that’s our new min  
end  
end

```
sorted << min #put the smallest in sorted
unsorted.delete(min) #delete it from unsorted

```

end

p sorted #all sorted!

* * *

The comments should help explain what’s going on. Note that I skip the  
first step (“get the smallest value from the original list, put that in  
sorted, put the rest in unsorted”) in the second example, because I copy  
the entire list into unsorted first.

Anyways, I hope that helps. You can probably come up with a better  
version!

-Justin

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 10:34pm UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/6 "2006-06-29T22:34:51Z")

</div>

I just started going through the replies, thank you all very much!  
Anyway, this one below, just kind of blows me away so succinct!  
I guess because it’s Ruby.

Stuart

On 6/29/06, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> \*\* more spoilers \*\*

---

<div class="post-metadata">

**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\
**Post date:** [June 29, 2006, 10:06am UTC](https://www.ruby-forum.com/t/re-sorting-arrays/96496/7 "2006-06-29T10:06:24Z")

</div>

\*\* more spoilers \*\*

2006/6/29, Justin C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> #if you can use Array#min:
> 
> list = [“aword”, “cword”, “gword”, “zword”, “dword”, “qword”, “pword”]  
> unsorted = []  
> sorted = []
> 
> sorted \<\< list.min #add the smallest to sorted  
> unsorted = list - sorted #add the rest to unsorted

This setup code above is superfluous.

> until unsorted.empty? #when unsorted is empty, we are done  
> sorted \<\< unsorted.min #put the smallest value into sorted  
> unsorted.delete(unsorted.min) #take it out of unsorted  
> end
> 
> p sorted #all sorted!

You can do

list = [“aword”, “cword”, “gword”, “zword”, “dword”, “qword”, “pword”]  
unsorted = list.dup  
sorted = []  
until unsorted.empty? #when unsorted is empty, we are done  
sorted \<\< unsorted.min #put the smallest value into sorted  
unsorted.delete(unsorted.min) #take it out of unsorted  
end  
p sorted

> * * *
> 
> #if you can’t use Array#min:

Here’s a shorter version using inject (of course): 🙂

require ‘enumerator’  
unsorted = list.dup  
sorted = []  
until unsorted.empty?  
min, pos = unsorted.  
to\_enum(:each\_with\_index).  
inject {|(minel, minidx), (el, idx)| el \< minel ? [el, idx] :  
[minel, minidx]}  
unsorted.delete\_at pos  
sorted \<\< min  
end  
p sorted

This is the more verbose but equivalent version:

unsorted = list.dup  
sorted = []

until unsorted.empty?  
min = pos = nil

unsorted.each\_with\_index do |el, idx|  
if min.nil? || el \< min  
min = el  
pos = idx  
end  
end

unsorted.delete\_at pos  
sorted \<\< min  
end  
p sorted

You can save one comparison op per loop if you do

unsorted = list.dup  
sorted = []  
until unsorted.empty?

# unsorted is not empty, so there is an element at pos 0!

min = unsorted[0]  
pos = 0

unsorted.each\_with\_index do |el, idx|  
if el \< min  
min = el  
pos = idx  
end  
end

unsorted.delete\_at pos  
sorted \<\< min  
end  
p sorted

Kind regards

robert