概述
列表（List）是App Inventor 2中最常用的数据结构。本文介绍列表的高级操作技巧，解决用户常见需求：
- 判断列表中有没有重复项
- 列表去重
- 列表排序
- 列表查找和过滤
- 列表交叉/差集操作
列表基础回顾
常用列表积木块
| 操作 | 积木块 | 说明 |
|---|---|---|
| 创建 | make a list | 创建列表 |
| 添加 | add items to list | 末尾添加元素 |
| 读取 | select list item | 按索引读取 |
| 长度 | length of list | 获取元素数量 |
| 是否在列表 | is in list? | 判断元素是否存在 |
| 索引 | index in list | 获取元素的索引 |
| 删除 | remove list item | 按索引删除 |
| 替换 | replace list item | 按索引替换 |
判断列表中有没有重复项
方法一：逐个比较
function hasDuplicate(list) {
var result = False
var i = 1
while i <= lengthOfList(list) - 1 {
var j = i + 1
while j <= lengthOfList(list) {
if selectListItem(list, i) == selectListItem(list, j) {
result = True
j = lengthOfList(list) + 1 // break
i = lengthOfList(list) + 1 // break
} else {
j = j + 1
}
}
i = i + 1
}
return result
}
方法二：利用字典去重后比较长度
function hasDuplicateByDict(list) {
var uniqueList = uniqueValues(list)
var result = False
if lengthOfList(uniqueList) < lengthOfList(list) {
result = True
} else {
result = False
}
return result
}
使用示例
when Button1.Click() {
var myList = createList("苹果", "香蕉", "橙子", "香蕉", "葡萄")
if hasDuplicate(myList) {
Label1.Text = "⚠️ 列表中有重复项"
} else {
Label1.Text = "✅ 列表中没有重复项"
}
}
列表去重
方法一：利用字典键去重（推荐）
字典的键是唯一的，可以巧妙地用来去重：
function uniqueValues(list) {
var uniqueList = createList()
var i = 1
while i <= lengthOfList(list) {
var currentItem = selectListItem(list, i)
if not(isItemInList(currentItem, uniqueList)) {
addItemsToList(uniqueList, currentItem)
}
i = i + 1
}
return uniqueList
}
方法二：保持顺序的去重
function uniqueValuesOrdered(list) {
var seen = createList()
var resultList = createList()
var i = 1
while i <= lengthOfList(list) {
var currentItem = selectListItem(list, i)
if not(isItemInList(currentItem, seen)) {
addItemsToList(seen, currentItem)
addItemsToList(resultList, currentItem)
}
i = i + 1
}
return resultList
}
获取重复项列表
function getDuplicates(list) {
var duplicates = createList()
var seen = createList()
var i = 1
while i <= lengthOfList(list) {
var currentItem = selectListItem(list, i)
if isItemInList(currentItem, seen) {
if not(isItemInList(currentItem, duplicates)) {
addItemsToList(duplicates, currentItem)
}
} else {
addItemsToList(seen, currentItem)
}
i = i + 1
}
return duplicates
}
统计每个元素出现次数
function countFrequencies(list) {
var frequencies = createDictionary()
var i = 1
while i <= lengthOfList(list) {
var currentItem = selectListItem(list, i)
if isDictionaryKey(frequencies, currentItem) {
var currentCount = getDictionaryValue(frequencies, currentItem)
setDictionaryValue(frequencies, currentItem, currentCount + 1)
} else {
setDictionaryValue(frequencies, currentItem, 1)
}
i = i + 1
}
return frequencies
}
列表排序
冒泡排序
function bubbleSort(list) {
var sortedList = copyList(list)
var n = lengthOfList(sortedList)
var i = 1
while i <= n - 1 {
var j = 1
while j <= n - i {
if selectListItem(sortedList, j) > selectListItem(sortedList, j + 1) {
// 交换
var temp = selectListItem(sortedList, j)
replaceListItem(sortedList, j, selectListItem(sortedList, j + 1))
replaceListItem(sortedList, j + 1, temp)
}
j = j + 1
}
i = i + 1
}
return sortedList
}
数字排序（从小到大）
function numericSort(list) {
var sortedList = copyList(list)
var n = lengthOfList(sortedList)
var i = 1
while i <= n - 1 {
var j = 1
while j <= n - i {
var a = selectListItem(sortedList, j)
var b = selectListItem(sortedList, j + 1)
if a > b {
var temp = selectListItem(sortedList, j)
replaceListItem(sortedList, j, selectListItem(sortedList, j + 1))
replaceListItem(sortedList, j + 1, temp)
}
j = j + 1
}
i = i + 1
}
return sortedList
}
列表查找和过滤
查找所有匹配项
function findAll(list, target) {
var result = createList()
var i = 1
while i <= lengthOfList(list) {
if selectListItem(list, i) == target {
addItemsToList(result, i)
}
i = i + 1
}
return result
}
按条件过滤
function filterGreaterThan(list, threshold) {
var result = createList()
var i = 1
while i <= lengthOfList(list) {
var val = selectListItem(list, i)
if val > threshold {
addItemsToList(result, selectListItem(list, i))
}
i = i + 1
}
return result
}
模糊搜索
function fuzzySearch(list, keyword) {
var result = createList()
var i = 1
while i <= lengthOfList(list) {
var currentItem = selectListItem(list, i)
if containsText(currentItem, keyword) {
addItemsToList(result, currentItem)
}
i = i + 1
}
return result
}
列表集合操作
交集（两个列表共同元素）
function intersectLists(listA, listB) {
var result = createList()
var i = 1
while i <= lengthOfList(listA) {
if isItemInList(selectListItem(listA, i), listB) {
addItemsToList(result, selectListItem(listA, i))
}
i = i + 1
}
return uniqueValues(result)
}
差集（在A但不在B中）
function listDifference(listA, listB) {
var result = createList()
var i = 1
while i <= lengthOfList(listA) {
if not(isItemInList(selectListItem(listA, i), listB)) {
addItemsToList(result, selectListItem(listA, i))
}
i = i + 1
}
return result
}
合并去重
function mergeUnique(listA, listB) {
var merged = copyList(listA)
appendListToList(merged, listB)
return uniqueValues(merged)
}
实用工具函数
列表转逗号分隔文本
function listToText(list, sep) {
var result = ""
var i = 1
while i <= lengthOfList(list) {
if i == 1 {
result = selectListItem(list, i)
} else {
result = join(result, sep, selectListItem(list, i))
}
i = i + 1
}
return result
}
列表最大值/最小值
function listMax(list) {
var maxVal = selectListItem(list, 1)
var i = 2
while i <= lengthOfList(list) {
var currentVal = selectListItem(list, i)
if currentVal > maxVal {
maxVal = currentVal
}
i = i + 1
}
return maxVal
}
常见问题
Q1: is in list 区分大小写吗？
是的，is in list 精确匹配，区分大小写。如果需要不区分大小写的查找：
function containsCaseInsensitive(list, target) {
var found = False
var i = 1
while i <= lengthOfList(list) {
if downcase(selectListItem(list, i)) == downcase(target) {
found = True
i = lengthOfList(list) + 1 // break
} else {
i = i + 1
}
}
return found
}
Q2: 如何随机打乱列表？
function randomShuffle(list) {
var result = copyList(list)
var i = lengthOfList(result)
while i > 1 {
var j = randomInteger(1, i)
var temp = selectListItem(result, i)
replaceListItem(result, i, selectListItem(result, j))
replaceListItem(result, j, temp)
i = i - 1
}
return result
}
总结
| 操作 | 时间复杂度 | 适用场景 |
|---|---|---|
| 判断重复 | O(n²) 或 O(n) | 数据验证 |
| 去重 | O(n²) | 数据清洗 |
| 排序 | O(n²) | 显示排序 |
| 查找 | O(n) | 搜索功能 |
| 过滤 | O(n) | 数据筛选 |
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