切片陣列陣列

Question

取樣陣列，

# 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]] 

現在，

arr.some_slicing_technique(0..2) 

應該給我，

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

是否some_slicing_technique存在嗎？解決這個問題的最好方法是什麼？

Answer 1

你可以這樣說：

[[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，如果你想使用範圍：

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

Answer 2

你可以調換原始數組，取出最後一塊再次調換它：

arr.transpose[0..2].transpose 

Answer 3

一點更通用：

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]]