How do I extract specific elements from an array?

问题

If I have an array a = [1,2,3,4,5,6,7,8,9,10] and I want a subset of this array - the 1st, 5th and 7th elements. Is it possible to extract these from this array in a simple way. I was thinking something like:

a[0,4,6] = [1,5,7]

but that doesn't work.

Also is there a way to return all indices except those specified? For example, something like

a[-0,-4,-6] = [2,3,4,6,8,9,10]

回答1:

Here's one way:

[0,4,6].map{|i| a[i]}

回答2:

You can simply do:

[1] pry(main)> [1,2,3,4,5,6,7,8,9,10].values_at(0, 4, 6)
=> [1, 5, 7]

回答3:

a = [1,2,3,4,5,6,7,8,9,10]

For a[0,4,6] = [1,5,7] :

a.values_at(0, 4, 6)
=> [1, 5, 7]

For a[-0,-4,-6] = [2,3,4,6,8,9,10] :

a - a.values_at(0, 4, 6)
=> [2, 3, 4, 6, 8, 9, 10]

回答4:

In Ruby, Array objects have a method/operator [] which allows you to get/reference an object at a specific index, or a contiguous subset of objects specified by a range.

ary[index] → obj or nil
ary[start, length] → new_ary or nil
ary[range] → new_ary or nil

Personally, I like your syntax. It would be useful but it is not provided by the standard Array object. Until Ruby adopts your syntax, as others have suggested, you have the values_at method to do exactly what you need.

values_at(selector,... ) → new_ary

If a = [1,2,3,4,5,6,7,8,9,10], then:

a.values_at(0, 4, 6)
=> [1, 5, 7]

来源：https://stackoverflow.com/questions/8921811/how-do-i-extract-specific-elements-from-an-array

标签

ruby

arrays

subset