在Swift中查找数组数组中的值（类似于Excel中的VLOOKUP函数） [英] Finding a value in an array of arrays (similar to VLOOKUP function in Excel) in Swift

问题描述

我对Swift 3和一般的编程语言还是陌生的。我在数组和变量收入中有以下数组：

I am quite new to Swift 3 and to programming languages in general. I have the following arrays inside an array and a variable income:

let testArray: [[Double]] = [
    [0,0],
    [1000,20.5],
    [3000,21],
    [4000,22.5],
   ]

var income: Double = 3500

我要执行的操作类似于Excel中的VLOOKUP函数：我想在数组的第一列（即0、1000、3000、4000）中找到一个等于或立即小于我的变量的数字。在这种情况下，当收入= 3500时，程序应返回3000。我尝试使用filter（），但是我不知道如何处理数组中的数组。感谢所有帮助。

What I want to do is something similar to the VLOOKUP function in Excel: I want to find in the first column of the arrays (i.e. 0, 1000, 3000, 4000) a number which is equal or immediately smaller than my variable. In this case, as income = 3500, the program should return 3000. I tried using filter() but I don't know how to work with the arrays inside the array. Any help appreciated.

推荐答案

您可以按照以下步骤进行操作。

You can proceed as follows.

获取数组的第一列：

let firstColumn = testArray.map { $0[0] }
print(firstColumn) // [0.0, 1000.0, 3000.0, 4000.0]

限制为小于或等于给定的
金额：

Restrict to those elements which are less than or equal to the given amount:

let filtered = firstColumn.filter { $0 <= income }
print(filtered) // [0.0, 1000.0, 3000.0]

获取最大的元素过滤后的数组。如果元素是按升序排序的
，则可以使用 last 代替 max（）：

Get the maximal element of the filtered array. If the elements are sorted in increasing order then you can use last instead of max():

let result = filtered.max()!
// Or: let result = filtered.last!
print(result) // 3000.0

将它们放在一起：

let result = testArray.map { $0[0] }.filter { $0 <= income }.max()!
print(result) // 3000.0

可能的优化是合并 map 和 filter 到
flatMap ：

A possible optimization is to combine map and filter into flatMap:

let result = testArray.flatMap { $0[0] <= income ? $0[0] : nil }.max()!
print(result) // 3000.0

此代码假定至少有一个匹配项元素，否则
否则 last！或 max（）！会崩溃。如果不能保证：

This code assumes that there is at least one matching element, otherwise last! or max()! would crash. If that is not guaranteed:

if let result = testArray.flatMap( { $0[0] <= income ? $0[0] : nil }).max() {
    print(result) // 3000.0
} else {
    print("no result")
}

或提供默认值（在此示例中为 0.0 ）：

Or provide a default value (0.0 in this example):

let result = testArray.flatMap( { $0[0] <= income ? $0[0] : nil }).max() ?? 0.0
print(result) // 3000.0

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