# Newbie - several array questions

**URL:** <https://www.ruby-forum.com/t/newbie-several-array-questions/160630>\
**Category:** Ruby\
**Created:** [February 18, 2009, 9:47am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630 "2009-02-18T09:47:34Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 9:47am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/1 "2009-02-18T09:47:34Z")

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Hi all - I’m a first-timer and very much love Ruby!

I have several questions involving arrays. First, I’ll create a couple  
of arrays to use in my examples -

arr1 = [1, 2, 3, 4, 5]  
arr2 = [“foo”, “bar”, “baz”, “abc”, “def”]

What I want to do is the following -  
a) I want to create another array that alternates the elements of these  
two arrays, like this -  
[1, “foo”, 2, “bar”, 3, “baz”, 4, “abc”, 5, "def]

b) In order to be able to create text tables, I’d like a function that  
can take a character (like “|”) and can apply it to an array so that you  
end up with another array like this -  
arr4 = ["|", “foo”, “|”, “bar”, “|”, “baz”, “|”]

c) Finally, I’d like to create another function to do a very similar  
thing to (b), but only have the character _between_ the elements, like  
this -  
arr5 = [“foo”, “|”, “bar”, “|”, “baz”]

Very many thanks in advance for your help! (Many thanks to Matz too  
for a great language! 🙂 )

- latte

---

<div class="post-metadata">

**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 10:32am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/2 "2009-02-18T10:32:50Z")

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Andy Elvey wrote:

> 

arr1 = [1, 2, 3, 4, 5]  
arr2 = [“foo”, “bar”, “baz”, “abc”, “def”]

resultA = arr1.zip(arr2).flatten

resultB = []  
arr2.each do |item|  
resultB \<\< “|” \<\< item  
end  
resultB \<\< “|”

resultC = []  
arr2.each do |item|  
resultC \<\< item \<\< “|”  
end  
resultC.pop()

p resultA  
p resultB  
p resultC

–output:–  
[1, “foo”, 2, “bar”, 3, “baz”, 4, “abc”, 5, “def”]  
["|", “foo”, “|”, “bar”, “|”, “baz”, “|”, “abc”, “|”, “def”, “|”]  
[“foo”, “|”, “bar”, “|”, “baz”, “|”, “abc”, “|”, “def”]

---

<div class="post-metadata">

**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 10:37am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/3 "2009-02-18T10:37:20Z")

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From: Andy Elvey [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

# arr1 = [1, 2, 3, 4, 5]

# arr2 = [“foo”, “bar”, “baz”, “abc”, “def”]

try #zip

eg,

> arr1.zip(arr2).flatten  
> =\> [1, “foo”, 2, “bar”, 3, “baz”, 4, “abc”, 5, “def”]

> Array.new(arr2.size+1,“|”).zip(arr2).flatten[0…-2]  
> =\> [“|”, “foo”, “|”, “bar”, “|”, “baz”, “|”, “abc”, “|”, “def”, “|”]

> arr2.zip(Array.new(arr2.size-1,“|”)).flatten[0…-2]  
> =\> [“foo”, “|”, “bar”, “|”, “baz”, “|”, “abc”, “|”, “def”]

---

<div class="post-metadata">

**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 11:20am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/4 "2009-02-18T11:20:09Z")

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2009/2/18 7stud – [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> resultB \<\< “|” \<\< item  
> end  
> resultB \<\< “|”

You can also write it using inject like this:  
arr = arr2.inject([“|”]){|r,e|r\<\<e\<\<“|”}

> resultC = []  
> arr2.each do |item|  
> resultC \<\< item \<\< “|”  
> end  
> resultC.pop()

arr = arr2.inject([]){|r,e|r\<\<e\<\<“I”}  
arr.pop

Regards,

Park H.

---

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**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 4:08pm UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/5 "2009-02-18T16:08:51Z")

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Heesob P. wrote:

> 2009/2/18 7stud – [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):
> 
> > resultB \<\< “|” \<\< item  
> > end  
> > resultB \<\< “|”
> 
> You can also write it using inject like this:  
> arr = arr2.inject([“|”]){|r,e|r\<\<e\<\<“|”}

As long as you realize that inject() is always the most inefficient  
solution possible.

---

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**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 10:48am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/6 "2009-02-18T10:48:32Z")

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7stud – wrote:

> arr1 = [1, 2, 3, 4, 5]  
> arr2 = [“foo”, “bar”, “baz”, “abc”, “def”]
> 
> resultA = arr1.zip(arr2).flatten

This is probably more efficient:

resultA = []  
arr1.zip(arr2) do |item\_arr1, item\_arr2|  
resultA \<\< item\_arr1 \<\< item\_arr2  
end

Just remember: a bunch of methods chained together on one line is rarely  
very efficient.

---

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**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 6:11pm UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/7 "2009-02-18T18:11:50Z")

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> As long as you realize that inject() is always the most inefficient  
> solution possible.

Can you elaborate on your claim? How inefficient, like, by orders of  
magnitude? Is it serious enough to affect the overall performance of a  
typical ruby application? In a situation like this, I’d prefer the  
code which uses ‘inject’, since it shows the intention of the  
programmer more clearly and concisely, while the performance penalty -  
10% in my naive experiment - is irrelevant in this case. I agree that  
we should be aware of the performance issues even when we’re dealing  
with a high-level language such as ruby, but your bold statement makes  
me feel that you’re trying to ‘defend’ your own code against the  
others in some kind of a code contest.

---

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**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 18, 2009, 7:32pm UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/8 "2009-02-18T19:32:43Z")

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On Wed, Feb 18, 2009 at 12:10 PM, Choi, Junegunn [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> 10% in my naive experiment - is irrelevant in this case. I agree that  
> we should be aware of the performance issues even when we’re dealing  
> with a high-level language such as ruby, but your bold statement makes  
> me feel that you’re trying to ‘defend’ your own code against the  
> others in some kind of a code contest.

I think that the statement that “inject() is always the inefficient  
solution  
possible”, even if it were true, which I’m not at all sure it is, isn’t  
particularly good advice.

One of my buddy Kent Beck’s more well known memes is “Make it run. Make  
it  
right, Make it fast.” [1]. Although the roots of this advice can be  
traced  
back to Butler Lampson [2]. This advice is something that anyone who  
wants  
to be a software craftsman needs to take to heart.

The order is important. First you make sure that the code runs, then  
you  
need to make it right. Making it right doesn’t mean that it does the  
right  
thing, that’s a large part of making it run, it mean’s making the code  
clear  
and maintainable, either by you sometime in the future, or by someone  
else.  
Only then you should make it fast, without unnecessarily harming keeping  
it  
right. And the best way to do this is to slavishly follow the 3 rules  
of  
optimization [3]

While there are some who just seem to hate inject, it can, as you point  
out,  
be much more intention revealing, which helps in making code right.

This is just one of those things, like when and when not to use optional  
parentheses in Ruby which need a bit of thoughtful reflection, rather  
than  
blind adherence to convention.

[1] [http://c2.com/cgi/wiki?MakeItWorkMakeItRightMakeItFast](http://c2.com/cgi/wiki?MakeItWorkMakeItRightMakeItFast)  
[2]  
[http://research.microsoft.com/en-us/um/people/blampson/33-hints/webpage.html](http://research.microsoft.com/en-us/um/people/blampson/33-hints/webpage.html)  
[3] [http://c2.com/cgi/wiki?RulesOfOptimization](http://c2.com/cgi/wiki?RulesOfOptimization)

–  
Rick DeNatale

Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)  
Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale)  
WWR: [http://www.workingwithrails.com/person/9021-rick-denatale](http://www.workingwithrails.com/person/9021-rick-denatale)  
LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)

---

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**Author:** ![latte](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/5e9695/32.png) [@latte](https://www.ruby-forum.com/u/latte)\
**Post date:** [February 19, 2009, 7:21am UTC](https://www.ruby-forum.com/t/newbie-several-array-questions/160630/9 "2009-02-19T07:21:13Z")

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Rick Denatale wrote:

> On Wed, Feb 18, 2009 at 12:10 PM, Choi, Junegunn [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > 10% in my naive experiment - is irrelevant in this case. I agree that  
> > we should be aware of the performance issues even when we’re dealing  
> > with a high-level language such as ruby, but your bold statement makes  
> > me feel that you’re trying to ‘defend’ your own code against the  
> > others in some kind of a code contest.
> 
> I think that the statement that “inject() is always the inefficient  
> solution possible”, even if it were true, which I’m not at all sure it is, isn’t particularly good advice.
> 
> One of my buddy Kent Beck’s more well known memes is “Make it run. Make  
> it  
> right, Make it fast.” [1]. Although the roots of this advice can be  
> traced  
> back to Butler Lampson [2]. This advice is something that anyone who  
> wants  
> to be a software craftsman needs to take to heart.

( snip )

Great! Oh, and please forgive me for snipping a few lines here, Rick -  
I got an automated message telling me to reduce the number of quoted  
lines.

Thanks Rick, and a very big **thank you** to everyone else who has  
replied here! It’s great to be part of such an active, friendly and  
generous community!

Bye for now - 🙂

- latte