需求
很简单的知识点，做一下小结。
最近写代码需要做一下切片的操作，比如给定这样一个切片：
lst1 = [1,2,3,4,5,6,7,8,9,10,11,12,13]
将这个切片里面的元素按照每4个为一组，每一组组成单独的切片，然后再组合到外层的切片中，结果像这样：
[[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13]]
python的写法
# -*- coding:utf-8 -*- lst1 = [1,2,3,4,5,6,7,8,9,10,11,12,13] lst2 = ["w","wg","wa","jj","aa","ff","gg","hh","asd","ww","ee","gg","nn","mm"] print(len(lst1)) # 13 print(len(lst2)) # 14 ### 超限切片 ret_lst1 = list() ret_lst2 = list() # 根据lst1构建新的列表 for i in range(0,len(lst1),4): curr_lst = lst1[i:i+4] ret_lst1.append(curr_lst) # 根据lst2构建新的列表 for i in range(0,len(lst2),4): curr_lst = lst2[i:i+4] ret_lst2.append(curr_lst) ### 注意结果最后一个列表不足的话不会报错 print(ret_lst1) # [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13]] print(ret_lst2) # [[\'w\', \'wg\', \'wa\', \'jj\'], [\'aa\', \'ff\', \'gg\', \'hh\'], [\'asd\', \'ww\', \'ee\', \'gg\'], [\'nn\', \'mm\']]
Go的写法
错误的写法
package t9 import ( "fmt" "testing" ) func TestOutRange(t *testing.T) { lst1 := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13} lst2 := []string{"w", "wg", "wa", "jj", "aa", "ff", "gg", "hh", "asd", "ww", "ee", "gg", "nn", "mm"} fmt.Println(len(lst1)) // 13 fmt.Println(len(lst2)) // 14 // 结果 var retLst1 [][]int var retLst2 [][]string // 超限切片 for i := 0; i < len(lst1); i += 4 { currLst := lst1[i : i+4] retLst1 = append(retLst1, currLst) } for i := 0; i < len(lst2); i += 4 { currLst := lst2[i : i+4] retLst2 = append(retLst2, currLst) } }
这样写会上报一个错误：
--- FAIL: TestOutRange (0.00s) panic: runtime error: slice bounds out of range [:16] with capacity 13 [recovered] panic: runtime error: slice bounds out of range [:16] with capacity 13
错误的原因是，我们每次获取currLst的时候，是按照 lst[i i+4] 这样直接切片的，但是，如果i+4大于列表lst的长度的话，会上报越界错误！
正确的写法 ***
既然i+4可能会超出lst的长度越界，那我们在切片的时候判断一下二者的大小即可：
package t9 import ( "fmt" "testing" ) // 返回两个int最小的那个 func minInt(a, b int) int { if a < b { return a } return b } func TestOutRange(t *testing.T) { lst1 := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13} lst2 := []string{"w", "wg", "wa", "jj", "aa", "ff", "gg", "hh", "asd", "ww", "ee", "gg", "nn", "mm"} fmt.Println(len(lst1)) // 13 fmt.Println(len(lst2)) // 14 // 结果 var retLst1 [][]int var retLst2 [][]string // 切片 for i := 0; i < len(lst1); i += 4 { // 保证不越界 currLst := lst1[i:minInt(i+4, len(lst1))] retLst1 = append(retLst1, currLst) } for i := 0; i < len(lst2); i += 4 { // 保证不越界 currLst := lst2[i:minInt(i+4, len(lst2))] retLst2 = append(retLst2, currLst) } // 注意结果有填充的默认值 fmt.Println(retLst1) // [[1 2 3 4] [5 6 7 8] [9 10 11 12] [13]] fmt.Println(retLst2) // [[w wg wa jj] [aa ff gg hh] [asd ww ee gg] [nn mm]] }
～～～
