What is wrong here

Hello,

I want to sort a hash by first the value and after that the key.

So I did this :

def solution(array, key)
array.sort_by{ |key,array[value]| key}
end

But now I see a syntaxt error

Roelof

You cant use argument array[value] in list of enumerate variables.
What is a array variable?

Addition documentation:
http://www.ruby-doc.org/core-2.1.1/Enumerable.html#method-i-sort_by

28 2014 ., 15:01, Roelof W. [email protected] ():

Evgeniy schreef op 28-5-2014 13:26:
You can?t use argument ?array[value]? in list of enumerate variables.
What is a ?array? variable??


28 ??? 2014 ?., ? 15:01, Roelof W. <rem[email protected]> ???????(?):


Array is hash which schould be sorted.
the key is the key which is sorted.

Roelof

For hash:
a = {:a => 6,:b =>5, :c =>4}
a.sort_by{|key,value| key} -> [[:a, 6], [:b, 5], [:c, 4]]
a.sort_by{|key,value| value} -> [[:c, 4], [:b, 5], [:a, 6]]

For array:
a = [6,2,7,9,4,2]
a.sort_by{|item| item} -> [2, 2, 4, 6, 7, 9]

For array of hashes:
a = [{:a => 1, :b => 4},{:a => 2, :b => 3}]

a.sort_by{|i| i[:a]} -> [{:a=>1, :b=>4}, {:a=>2, :b=>3}]
a.sort_by{|i| i[:b]} -> [{:a=>2, :b=>3}, {:a=>1, :b=>4}]

28 2014 ., 15:42, Roelof W. [email protected] ():

Roelof W. schreef op 28-5-2014 13:34:
Evgeniy schreef op 28-5-2014 13:26:
You can?t use argument ?array[value]? in list of enumerate variables.
What is a ?array? variable??


28 ??? 2014 ?., ? 15:01, Roelof W. <[email protected]>
        ???????(?):</div>
      <br>
    </div>
  </blockquote>
  <br>
  Array is hash which schould be sorted.<br>
  the key is the key which is sorted. <br>
  <br>
  Roelof<br>
  <br>
</blockquote>
<br>
Found it but not complete right.<br>
<br>
?array.sort_by{|key|array} <br>
<br>
But then the sort has the wrong order 2 is now before 1 <br>
<br>
Roelof<br>
<br>
<br>

Oh… now I see what you want.

def solution(array_of_hashes, key)
array_of_hashes.sort{|x,y| x[key] <=> y[key] }
end

One example:

hash = [{id: 2}, {id: 1}]
solution(a,:id) -> [{id: 1}, {id: 2}]

Two example:

hash = [{:a=>1, :b=>4}, {:a=>2, :b=>3}]
solution(hash,:a) -> [{:a=>1, :b=>4}, {:a=>2, :b=>3}]
solution(hash,:b) -> [{:a=>2, :b=>3}, {:a=>1, :b=>4}]

28 2014 ., 16:09, Roelof W. [email protected] ():

Evgeniy wny not?

def solution(array_of_hashes, key)
array_of_hashes.sort_by{|h| h[key] }
end

Evgeniy schreef op 28-5-2014 13:55:
sort_by{|key,value| key}


Still not working.

I have now :

def solution(array, key)
??? array.sort_by{|key,value| key}
end

And as test :

one, two = [{id: 1}, {id: 2}]
Test.assert_equals(solution([two, one], :id), [one, two])

but I see this error message :

TypeError: no implicit conversion from nil to integer

Roelof



On Wed, May 28, 2014 at 2:09 PM, Roelof W. [email protected] wrote:

def solution(array, key)
TypeError: no implicit conversion from nil to integer

Roelof

You have an array of hashes. Each element of the array has a value by
which you want to sort. The method sort_by passes to the block each
element to compute a value by which to sort. So, the sort_by block
will receive each hash in turn. In the hash, you want to extract the
value for the :id key, to sort by that. So:

2.0.0p195 :001 > one, two = [{id: 1}, {id: 2}]
=> [{:id=>1}, {:id=>2}]
2.0.0p195 :002 > [one, two].sort_by {|h| h[:id]}
=> [{:id=>1}, {:id=>2}]

If you want to make it a method and specify a different key within the
hash to sort every time, you can do it like this:

2.0.0p195 :006 > def solution array_of_hashes, key
2.0.0p195 :007?> array_of_hashes.sort_by {|h| h[key]}
2.0.0p195 :008?> end
=> nil
2.0.0p195 :009 >
2.0.0p195 :010 > one, two = [{id: 1, weight: 10}, {id: 2, weight: 5}]
=> [{:id=>1, :weight=>10}, {:id=>2, :weight=>5}]
2.0.0p195 :011 > solution [one,two], :id
=> [{:id=>1, :weight=>10}, {:id=>2, :weight=>5}]
2.0.0p195 :012 > solution [one,two], :weight
=> [{:id=>2, :weight=>5}, {:id=>1, :weight=>10}]

Hope this helps,

Jesus.

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