ruby:如何在数组中查找非唯一元素并使用出现次数打印每个元素？

Question

我有

a = ["a", "d", "c", "b", "b", "c", "c"]

并且需要打印类似的东西(按出现次数降序排序):

c:3
b:2

我理解第一部分(发现非独特)是:

b = a.select{ |e| a.count(e) > 1 }
=> ["c", "b", "b", "c", "c"] 

要么

puts b.select{|e, c| [e, a.count(e)] }.uniq

c
b

如何输出每个非唯一的向后排序的出现次数？

Answer 1

puts a.uniq.
       map { | e | [a.count(e), e] }.
       select { | c, _ | c > 1 }.
       sort.reverse.
       map { | c, e | "#{e}:#{c}" }

Answer 2

该group_by方法通常用于此:

a.group_by{ |i| i }
{
    "a" => [
        [0] "a"
    ],
    "d" => [
        [0] "d"
    ],
    "c" => [
        [0] "c",
        [1] "c",
        [2] "c"
    ],
    "b" => [
        [0] "b",
        [1] "b"
    ]
}

我喜欢:

a.group_by{ |i| i }.each_with_object({}) { |(k,v), h| h[k] = v.size }
{
    "a" => 1,
    "d" => 1,
    "c" => 3,
    "b" => 2
}

要么:

Hash[a.group_by{ |i| i }.map{ |k,v| [k, v.size] }]
{
    "a" => 1,
    "d" => 1,
    "c" => 3,
    "b" => 2
}

其中一个可能会刮伤你的痒.从那里你可以使用一点测试来减少结果:

Hash[a.group_by{ |i| i }.map{ |k,v| v.size > 1 && [k, v.size] }]
{
    "c" => 3,
    "b" => 2
}

如果您只想打印信息,请使用:

puts a.group_by{ |i| i }.map{ |k,v| "#{k}: #{v.size}" }
a: 1
d: 1
c: 3
b: 2