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首页 > 解决方案 > 如何 gsub 匹配字符串并同时删除不匹配的字符串？

r - 如何 gsub 匹配字符串并同时删除不匹配的字符串？

问题描述

我有一个包含一列字符串的数据框，我想将其进一步标记为以下类别：城市、国家和大陆。我使用 gsub 将所有城市替换为“City”，将所有国家替换为“Country”，将所有大陆替换为“Continent”。

#This is what I have
dataframe
Color     Letter     Words
red       A          Paris,Asia,parrot,Antarctica,North America,cat,lizard
blue      A          Panama,New York,Africa,dog,Tokyo,Washington DC,fish
red       B          Copenhagen,bird,USA,Japan,Chicago,Mexico,insect
blue      B          Israel,Antarctica,horse,South America,North America,turtle,Brazil

#This is what I want
dataframe
Color     Letter     New
red       A          City,Continent
blue      A          Country,City,Continent
red       B          City,Country
blue      B          Country,Continent


#This is the code I have so far
dataframe$New <- NA

#groups all the cities
dataframe$New <- lapply)dataframe$Words, function(x) {
   gsub("Paris|New York|Tokyo|Washington DC|Copenhagen|Chicago", "City", x)})

#groups all the countries
dataframe$New <- lapply)dataframe$Words, function(x) {
   gsub("Panama|USA|Japan|Mexico|Israel|Brazil", "Country", x)})

#groups all the continents
dataframe$New <- lapply)dataframe$Words, function(x) {
   gsub("Asia|Antarctica|Africa|North America|South America", "Continent", x)})

dataframe$Words <- NULL

如何防止每次都覆盖 dataframe$New 以及如何删除多余的单词（即鱼、马、猫）？

上面的数据是一个基于非常大的数据集的例子。在数据集中，单词列有很多重复。有关 dataframe$Words 中的一些示例行，请参见下文：

Words
Panama,Paris
Panama,Israel,cat
Panama,Paris,horse,
Panama,Asia
Panama
Panama,Chicago
Israel,Chicago
Israel,lizard,Paris
Israel,Panama,horse,Africa
```

标签： rlapplygsub

解决方案

考虑粘贴几个ifelse检查特定字符串的调用：

dataframe$New <- paste(ifelse(grepl("Paris|New York|Tokyo|Washington DC|Copenhagen|Chicago", dataframe$Words), "City", "N/A"), 
                       ifelse(grepl("Panama|USA|Japan|Mexico|Israel|Brazil", dataframe$Words), "Country", "N/A"),
                       ifelse(grepl("Asia|Antarctica|Africa|North America|South America", dataframe$Words), "Continent", "N/A"),
                       sep=",")

dataframe$New <- gsub("N/A,|,N/A", "", dataframe$New)

dataframe

#   Color Letter                                                             Words                    New
# 1   red      A             Paris,Asia,parrot,Antarctica,North America,cat,lizard         City,Continent
# 2  blue      A               Panama,New York,Africa,dog,Tokyo,Washington DC,fish City,Country,Continent
# 3   red      B                   Copenhagen,bird,USA,Japan,Chicago,Mexico,insect           City,Country
# 4  blue      B Israel,Antarctica,horse,South America,North America,turtle,Brazil      Country,Continent

do.call或带有+的烘干机版本lapply：

strs <- list(c("Paris|New York|Tokyo|Washington DC|Copenhagen|Chicago", "City"),
             c("Panama|USA|Japan|Mexico|Israel|Brazil", "Country"),
             c("Asia|Antarctica|Africa|North America|South America", "Continent"))

df$New2 <- do.call(paste,
                   c(lapply(strs, function(s) ifelse(grepl(s[1], df$Words), s[2], "N/A")), 
                     list(sep=",")))
df$New2 <- gsub("N/A,|,N/A", "", df$New2)

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