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I have an array of hashes like so:
[{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]
And I'm trying to map this onto single hash like this:
{"testPARAM2"=>"testVAL2", "testPARAM1"=>"testVAL1"}
I have achieved it using
par={}
mitem["params"].each { |h| h.each {|k,v| par[k]=v} }
But I was wondering if it's possible to do this in a more idiomatic way (preferably without using a local variable).
How can I do this?
438
Method 2: Use the inject method Hash#merge creates a new hash on each iteration. For bigger arrays, it is more performant to use Hash#merge! / Hash#update .
The way the map method works in Ruby is, it takes an enumerable object, (i.e. the object you call it on), and a block. Then, for each of the elements in the enumerable, it executes the block, passing it the current element as an argument. The result of evaluating the block is then used to construct the resulting array.
In arrays, you have to loop over all items before you find what you are looking for while in a hash table you go directly to the location of the item. Inserting an item is also faster in Hash tables since you just hash the key and insert it.
Creating a Hash In Ruby you can create a Hash by assigning a key to a value with => , separate these key/value pairs with commas, and enclose the whole thing with curly braces.
You could compose Enumerable#reduce and Hash#merge to accomplish what you want.
input = [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]
input.reduce({}, :merge)
is {"testPARAM2"=>"testVAL2", "testPARAM1"=>"testVAL1"}
Reducing an array sort of like sticking a method call between each element of it.
For example [1, 2, 3].reduce(0, :+) is like saying 0 + 1 + 2 + 3 and gives 6.
In our case we do something similar, but with the merge function, which merges two hashes.
[{:a => 1}, {:b => 2}, {:c => 3}].reduce({}, :merge)
is {}.merge({:a => 1}.merge({:b => 2}.merge({:c => 3})))
is {:a => 1, :b => 2, :c => 3}
How about:
h = [{"testPARAM1"=>"testVAL1"}, {"testPARAM2"=>"testVAL2"}]
r = h.inject(:merge)
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