swift stride函数 数组分割 分组

stride函数，为可变步长类型值的序列

其中from to，最后一个值将会小(大)于to的值

for index in stride(from:0, to:3, by:1)  {
    print(index)
}
// print 0, 1, 2

for index in stride(from:3, to:0, by:-1) {
    print(index)
}
// print 3，2，1

而from through，最后一个值将会小(大)于等于through的值

for index in stride(from:0, through:3, by:1)  {
    print(index)
}
// print 0, 1, 2, 3

for index in stride(from:3, through:0, by:-1)  {
    print(index)
}
// print 3，2，1，0

调整by参数(步长)

for index in stride(from: 0, to: 9, by: 3) {
    print(index)
}
// print 0, 3, 6

//  through，包含末尾
for index in stride(from: 0, through: 9, by: 3) {
  print(index)
}
// prints 0, 3, 6, 9

数组分割
ps:步长与数组元素个数刚好整数倍，否则多出的元素会舍去

var array = Array(1...10)
let group1Arr = stride(from: 0, to: 8, by: 4).map {
    print(array[$0...$0+3])
}
//[1, 2, 3, 4]
//[5, 6, 7, 8]

let group2Arr = stride(from: 0, to: 8, by: 4).map {
      Array(array[$0...$0+3])
}
print(group2Arr) 
// [[1, 2, 3, 4], [5, 6, 7, 8]]

或

let step = 3
let finalArray = stride(from: 0, to: array.endIndex - (array.endIndex % step), by: step).map {
    Array(array[$0...$0+(step - 1)])
}
// step = 2
// [[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]
// step = 3
// [[1, 2, 3], [4, 5, 6], [7, 8, 9]]