I want to push more arrays into this Hash? - arrays

Question

i want to push an array into this part, i'm a newbie in Ruby
#edge_weights = {[position, position2] => node_distance}
That is a Hash? i think i want to push some other hashes of the same way to have a result like this:
{["1", "2"]=>2445, ["2", "3"]=>2015, ["2", "4"]=>1547, ["3", "4"]=>939, ["5", "1"]=>1548}
Not like this:
{["1", "2"]=>111},{["2", "3"]=>222},{["1", "3"]=>333}
How can i achieve this?. Sorry for my bad english :(

Answer 1

Presumably you will begin with some data such as the following array of arrays:
arr = [["1", "2", 2445], ["2", "3", 2015], ["2", "4", 1547],
["3", "4", 939], ["5", "1", "7", 1548], ["1", "2", -71]]
Step one is to create an empty hash:
h = {}
Now iterate over the elements of arr to build the hash h.
arr.each do |a|
*first, last = a
h[first] = last
end
#=> [["1", "2", 2445], ["2", "3", 2015], ["2", "4", 1547],
# ["3", "4", 939], ["5", "1", "7", 1548], ["1", "2", -71]]
We want the value of h, not the above return value.
h #=> {["1", "2"]=>-71, ["2", "3"]=>2015, ["2", "4"]=>1547,
# ["3", "4"]=>939, ["5", "1"]=>1548, ["5", "1", "7"]=>1548}
Note that Ruby's splat operator1 is used to break up an array in various ways:
*first, last = ["5", "1", "7", 1548]
first
#=> ["5", "1", "7"]
last
#=> 1548
Is the result above for h what you were expecting? Recall that hashes have unique keys. After the first element of arr is passed to the block we execute
h[["1", "2"]] = 2445
so that h becomes { ["1", "2"]=>2445 }. Later, when the last element of arr--which has the same key (["1", "2"])--is passed to the block, we execute
h[["1", "2"]] = -71
which overwrites the value of that key. If you'd prefer to keep the value of the first key encountered you could write
arr.each do |a|
*first, last = a
h[first] = last unless h.key?(first)
end
See Hash#key? (aka, has_key? and include?). (Aside: you could write ...if !h.key?(first), ! read not, but it's generally clearer to avoid negation by using unless.)
The "Ruby way" of writing the original construct is to use the method Enumerable#each_with_object and to splat the block variables a:
arr.each_with_object({}) do |(*first, last),h|
h[first] = last
end
#=> {["1", "2"]=>-71, ["2", "3"]=>2015, ["2", "4"]=>1547,
# ["3", "4"]=>939, ["5", "1"]=>1548, ["5", "1", "7"]=>1548}
This avoids the need to use a separate statement to create an empty hash and the code block returns the value of h.
(Don't worry if you don't understand this.)
One other common way to construct a hash is to use the method Hash#update (aka merge!):
arr.each_with_object({}) do |(*first, last),h|
h.update({ first=>last })
end
Note Ruby allows a shorthand version of the second line:
h.update(first=>last)
1 See "Multiple variable assignment" here.

Answer 2

you can pass array as key and assign value to it:
> edge_weights = {}
> edge_weights[["1","2"]] = 2445
> edge_weights[["2", "4"]] = 1547
> edge_weights
#=> {["1", "2"]=>2445, ["2", "4"]=>1547}