Two-dimensional array in Ruby

Question

Two-dimensional array in Ruby

Navigation

#1 by (4 votes)
#2 by (1 votes)

2

I have the two-dimensional array

a = [[1,'a'],[1,'b'],[2,'c'],[2,'d'],[3,'e'],[3,'f'],[4,'g'],[4,'h']]

I want to separate the letters in another array b so that it looks like this:

[["a","b"], ["c", "d"], ["e", "f"], ["g", "h"]]

Where the contents of each index of the new array (Ex: ["a", "b"] matches the first array item a ( a[0][0] and a[1][0] ... etc), I did this to try to solve the question:

first created the two-dimensional array
```
for i in (1..4)
  b[i] = Array.new
end
```

Then the code

c = 0
x = 0
a.each do |k|
  if  k[0] == a[x+1][0]
    b[k[0]][c] = k[1]
    c += 1
    x += 1
  else      
    b[k[0]][c] = k[1]
    c = 0
  end
end

The problem is the index 'c' that from the third index of the array b, is going to index 2 and the next the 4 in progression coming out like this ...

[nil, ["a", "b"], ["c", "d"], [nil, nil, "e", "f"], [nil, nil, nil, nil, "g", "h"]]

I think it may be a simple thing in this index, but I'm already mixing things up.

ruby-on-rails ruby

asked by anonymous 21.05.2014 / 03:54

2 answers

1

The beautiful ruby is that almost all of these types of processing can be written in a row, without using loops directly. It's like working with a functional language. Note:

a = [[1,'a'],[1,'b'],[2,'c'],[2,'d'],[3,'e'],[3,'f'],[4,'g'],[4,'h']]
result = a.inject([]) {|r, k| r[k[0]] ||= []; r[k[0]] << k[1]; r }

Inject serves to construct a value iteratively. You pass the value as argument and, at each iteration, it receives the current value and an argument and must return the next value. A little more explained:

result = a.inject([]) do |temp, element|
   index, value = element
   temp[index] ||= []
   temp[index] << value
   temp
end

You can also use inject! to apply the inplace modification.

21.05.2014 / 15:09

ServerSocket and Socket How to download images sequentially from a website using WGet?

score 4 · Accepted Answer

Try to use less index manipulation, which makes the code confusing. Usually Ruby allows this.

The code below creates elements in b for each index found in a elements. Then it adds to that element in b the elements found in a to that index.

a = [[1,'a'],[1,'b'],[2,'c'],[2,'d'],[3,'e'],[3,'f'],[4,'g'],[4,'h']] 
b = Array.new
a.each do |k|
  b[k[0]] ||= Array.new
  b[k[0]] << k[1]
end
b # => [nil, ["a", "b"], ["c", "d"], ["e", "f"], ["g", "h"]]