切片数组

Question

示例数组，

# sub-arrays are all of the same length
arr = [[1,2,3,4], [5,6,7,8], [2,4,6,8], [1,3,5,7]]

现在，

arr.some_slicing_technique(0..2)

应该给我，

[[1,2,3], [5,6,7], [2,4,6], [1,3,5]]

some_slicing_technique是否存在？解决这个问题的最佳方法是什么？

Answer 1

你可以这样做：

[[1,2,3,4], [5,6,7,8], [2,4,6,8], [1,3,5,7]].map {|e| e.take(3)}

=> [[1, 2, 3], [5, 6, 7], [2, 4, 6], [1, 3, 5]]

或者如果你想使用范围：

[[1,2,3,4], [5,6,7,8], [2,4,6,8], [1,3,5,7]].map {|e| e[0..2]}

Answer 2

您可以转置原始数组，删除最后一个块并再次转置它：

arr.transpose[0..2].transpose

Answer 3

更通用一点：

arr = [[1,2,3,4], [5,6,7,8], [2,4,6,8], [1,3,5,7]]
slice_lambda = lambda { |r| lambda{ |x| x[r]} }
arr.map(&slice_lambda[0..2])
# => [[1, 2, 3], [5, 6, 7], [2, 4, 6], [1, 3, 5]]
arr.map(&slice_lambda[1..2])
# => [[2, 3], [6, 7], [4, 6], [3, 5]]