Remove one level of a nested array

Question

How can you change this array:

[["1","one"], ["2","two"], ["3","three"]]

to this?

["1","one"], ["2","two"], ["3","three"]

Clarification

My apologies for giving an invalid second version. This is what I'm really going for:

I want to add ["0","zero"] to the beginning of [["1","one"], ["2","two"], ["3","three"]], to get:

[["0","zero"], ["1","one"], ["2","two"], ["3","three"]]

I have tried:

["0","zero"] << [["1","one"], ["2","two"], ["3","three"]]

The above approach produces this, which contains a nesting I don't want:

[["0","zero"], [["1","one"], ["2","two"], ["3","three"]]]

Is it possible you meant [{"1"=>"one"}, {"2"=>"two"}, {"3"=>"three"}] — Itay Moav -Malimovka
– Itay Moav -Malimovka, Commented May 19, 2011 at 23:39
@mathepic, @ItayMoav - I just clarified my question. My apologies for not being clearer. — sscirrus
– sscirrus, Commented May 19, 2011 at 23:46
I think you should show some source code. I think it would help if we looked at how you are building the array in the first place. I suspect a misuse of << when you probably should use += instead. — the Tin Man
– the Tin Man, Commented May 20, 2011 at 0:03
I am trying to reach the same thing and I am stuck here... I am trying exactly now to make [[1,"A"],[2,"B"],[3,"C"],[4,"D"],[5,"E"]] into [1,"A"],[2,"B"],[3,"C"],[4,"D"],[5,"E], I remind that I already did one day it but I don't remember how could I do that, I was to open another topic here at SO but I saw you now and I am trying to take opportunity of the doubt, I have tried flatten but it returns me [1,"A",2,"B",3,"C",4,"D",5,"E] and not [1,"A"],[2,"B"],[3,"C"],[4,"D"],[5,"E] — theEarlyRiser
– theEarlyRiser, Commented Aug 9, 2021 at 18:27

Wayne Conrad · Accepted Answer · 2011-05-19 23:58:15Z

7

unshift ought to do it for you:

a = [["1","one"], ["2","two"], ["3","three"]]
a.unshift(["0", "zero"])
=> [["0", "zero"], ["1", "one"], ["2", "two"], ["3", "three"]]

edited May 19, 2011 at 23:58

answered May 19, 2011 at 23:41

Wayne Conrad

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4 Comments

sscirrus Over a year ago

@WayneConrad - almost there. When I do this: [["Inbox", 0]] << current_user.folders.collect{|folder| [folder.name, folder.id]}.flatten(1), I get: [["Inbox", 0], ["My Folder", 132, "Fourth Folder", 133, "Third Folder", 134, "Fifth Folder", 135, "6th Folder", 136]]

Wayne Conrad Over a year ago

@Andrew Grimm, the flatten(1) is gone (the OP changed the question), so you can take away the +1 if you like :)

sscirrus Over a year ago

@WayneConrad - I still appreciate the flatten(1). Thank you very much for that.

sscirrus Over a year ago

@WayneConrad - that's it! Thank you very much and sorry for that sloppy first question. +1

Amokrane Chentir · Accepted Answer · 2011-05-19 23:34:19Z

5

You are probably looking for flatten:

Returns a new array that is a one-dimensional flattening of this array (recursively). That is, for every element that is an array, extract its elements into the new array. If the optional level argument determines the level of recursion to flatten.

[["1","one"], ["2","two"], ["3","three"]].flatten

Which gives you:

=> ["1", "one", "2", "two", "3", "three"]

answered May 19, 2011 at 23:34

Amokrane Chentir

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1 Comment

theEarlyRiser Over a year ago

And to unnest the first array level?? I have tried flatten as how you showed but it returns me [1,"one",2,"two",3,"three"] and not [1,"one"],[2,"two"],[3,"three"]!

kuriouscoder · Accepted Answer · 2011-05-19 23:36:09Z

3

[["1","one"], ["2","two"], ["3","three"]].flatten

answered May 19, 2011 at 23:36

kuriouscoder

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Comments

Andrew Grimm · Accepted Answer · 2011-05-20 00:03:01Z

0

You need to make your questions clearer, but is the following what you meant?

# Right answer
original = [["1","one"], ["2","two"]]
items_to_add = [["3","three"], ["4","four"]]
items_to_add.each do |item|
  original << item
end
original # => [["1", "one"], ["2", "two"], ["3", "three"], ["4", "four"]]

# Wrong answer
original = [["1","one"], ["2","two"]]
items_to_add = [["3","three"], ["4","four"]]
original << items_to_add # => [["1", "one"], ["2", "two"], [["3", "three"], ["4", "four"]]]

answered May 20, 2011 at 0:03

Andrew Grimm

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1 Comment

sscirrus Over a year ago

Thanks a lot Andrew. WayneConrad got the answer I was looking for using unshift. For posterity I've further clarified my original question.

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