array to hash on ruby

Question

I have code like this:

combinedbooks = [[
  "0000A|0000B",
  "0000A|0000D",
  "0000B|0000D"
]]

h = Hash[combinedbooks.map {|x| [x, 1]}]

The result is:

{["0000A|0000B", "0000A|0000D", "0000B|0000D"]=>1}

What I want to have is the following:

{["0000A|0000B"]=>1, ["0000A|0000D"]=>1, ["0000B|0000D"]=>1}

I cant figure out whats the problem, I believe that there is a problem with the array declaration but im not sure about it

What you want seems to be a mapping of single-item arrays to values. Why would you want that? — user229044
– user229044 ♦, Commented Dec 9, 2014 at 17:59
Why do you have a single-element array of array? That has code smell hinting the generation of the array is wrong. Perhaps if that was fixed then the rest of the problem would be a lot easier to solve. — the Tin Man
– the Tin Man, Commented Dec 9, 2014 at 23:52
@theTinMan I am creating an array of arrays I think that is why. Im not sure how to just push elements of one array into another without creating an array of arrays — user3540466
– user3540466, Commented Dec 10, 2014 at 9:04
I added an answer to help explain the difference between a push/append vs. a concatenate/add. — the Tin Man
– the Tin Man, Commented Dec 10, 2014 at 21:27

user229044 · Accepted Answer · 2014-12-09 19:39:18Z

2

If you want the keys to be single-item arrays, make them arrays:

arr = ["0000A|0000B", "0000A|0000D", "0000B|0000D"]

Hash[arr.map { |x| [[x], 1] }]

# => {["0000A|0000B"]=>1, ["0000A|0000D"]=>1, ["0000B|0000D"]=>1}

The format of your input has changed to a doubly-nested array. If that's accurate, simply use my solution, but map the first element of your array instead of the top-most array:

combinedbooks = [[ "0000A|0000B", "0000A|0000D", "0000B|0000D" ]]

Hash[combinedbooks[0].map { |x| [[x], 1] }]

# => {["0000A|0000B"]=>1, ["0000A|0000D"]=>1, ["0000B|0000D"]=>1}

edited Dec 9, 2014 at 19:39

answered Dec 9, 2014 at 18:00

user229044♦

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5 Comments

user229044 Over a year ago

@user3540466 the output is completely identical to your expected output, except that your expected output contains a syntax error that I assumed was a typo.

Max Over a year ago

@meagar The only way to get the incorrect output in the question is if combinedbooks is a nested Array. I think that is the source of confusion.

user3540466 Over a year ago

u r right there is a problem with my array definition (that I cant figure out) not with making the hash, sorry

user3540466 Over a year ago

@meagar could u explain a little bit further why a [0]. What is it exactly refering to?

user229044 Over a year ago

@user3540466 You have an array inside an array. Something like x = [[1]]. If you access x, you're getting the value [[1]] back. If you want to get at the 1, you can't use x[0], that just returns the inner array, [1]. To get at the 1, you need x[0][0]. Similarly, you have an array inside an array: combinedbooks = [[ "0000A|0000B", "0000A|0000D", "0000B|0000D" ]]. To get at your array of values, you can't just use combinedbooks, that variable holds a one-item array. You need combinedbooks[0] to access the inner array of three items.

the Tin Man · Accepted Answer · 2014-12-10 21:25:57Z

0

Im not sure how to just push elements of one array into another without creating an array of arrays

There are two ways people usually append to an array, and it's important to understand the difference between them. Meditate on these:

Append/push an array to another array using << results in a sub-array:

foo = []
foo << [1]
foo # => [[1]]

Concatenate/Add an array to another array using += results in the elements of the second array being appended, not the array itself:

foo = []
foo += [1]
foo # => [1]

answered Dec 10, 2014 at 21:25

the Tin Man

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