[英]Add values of same Key in array of hashes
Trying to add values of same key but with iterating it. 尝试添加相同键的值,但要对其进行迭代。 here is my array
这是我的数组
arr = [ {a: 10, b: 5, c: 2}, {a: 5, c: 3}, { b: 15, c: 4}, {a: 2}, {} ]
Want to converted it like 想将其转换为
{a: 17, b: 20, c: 9}
Here is one way to do this by making use of Enumerable#reduce
and Hash#merge
: 这是通过使用
Enumerable#reduce
和Hash#merge
做到这一点的一种方法:
arr.reduce {|acc, h| acc.merge(h) {|_,v1,v2| v1 + v2 }}
#=> {:a=>17, :b=>20, :c=>9}
each_with_object
to the rescue: each_with_object
进行救援:
result = arr.each_with_object(Hash.new(0)) do |hash, result|
hash.each { |key, value| result[key] += value}
end
p result
#1 Use a "counting hash" #1使用“计数哈希”
Edit: I just noticed that @Pascal posted the same solution earlier. 编辑:我只是注意到@Pascal早些时候发布了相同的解决方案。 I'll leave mine for the explanation.
我将离开我的解释。
arr.each_with_object(Hash.new(0)) { |h,g| h.each { |k,v| g[k] += v } }
#=> {:a=>17, :b=>20, :c=>9}
h = Hash.new(0)
is a counting hash with a default value of zero. h = Hash.new(0)
是默认值为零的计数哈希。 That means that if h
does not have a key k
, h[k]
returns zero (but the hash is not altered). 这意味着,如果
h
没有键k
,则h[k]
返回零(但哈希值不会改变)。 Ruby expands h[k] += 4
to h[k] = h[k] + 4
, so if h
does not have a key k
, h[k]
on the right side of the equality equals zero. Ruby将
h[k] += 4
扩展为h[k] = h[k] + 4
,因此,如果h
没有键k
,则等式右侧的h[k]
等于零。
#2 Use Hash#update #2使用哈希值#update
Specifically, use the form of this method (aka merge!
) that employs a block to determine the values of keys that are present in both hashes being merged. 具体来说,使用此方法的形式(也称为
merge!
),该方法采用一个块来确定要合并的两个哈希中都存在的键的值。
arr.each_with_object({}) { |h,g| g.update(h) { |_,o,n| o+n } }
#=> {:a=>17, :b=>20, :c=>9}
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