Question

在引用值列表时是否可以使用 grepl 参数，可能使用％in％运算符？我想采取下面的数据，如果动物名称有＆＃34;狗＆＃34;或者＆＃34; cat＆＃34;在其中，我想要返回一定的值，比如，＆＃34; keep＆＃34 ;;如果它没有＆＃34; dog＆＃34;或者＆＃34; cat＆＃34;，我想返回＆＃34;丢弃＆＃34;。

data <- data.frame(animal = sample(c("cat","dog","bird", 'doggy','kittycat'), 50, replace = T))

现在，如果我只是通过严格匹配值来做到这一点，比如说，＆＃34; cat＆＃34;和＆＃34; dog＆＃39;，我可以使用以下方法：

matches <- c("cat","dog")

data$keep <- ifelse(data$animal %in% matches, "Keep", "Discard")

但是使用grep或grepl只引用列表中的第一个参数：

data$keep <- ifelse(grepl(matches, data$animal), "Keep","Discard")

返回

Warning message:
In grepl(matches, data$animal) :
  argument 'pattern' has length > 1 and only the first element will be used

注意，我在搜索中看到了这个帖子，但这似乎不起作用： grep using a character vector with multiple patterns

Answer 1

您可以在|的正则表达式中使用“或”（grepl）语句。

ifelse(grepl("dog|cat", data$animal), "keep", "discard")
# [1] "keep"    "keep"    "discard" "keep"    "keep"    "keep"    "keep"    "discard"
# [9] "keep"    "keep"    "keep"    "keep"    "keep"    "keep"    "discard" "keep"   
#[17] "discard" "keep"    "keep"    "discard" "keep"    "keep"    "discard" "keep"   
#[25] "keep"    "keep"    "keep"    "keep"    "keep"    "keep"    "keep"    "keep"   
#[33] "keep"    "discard" "keep"    "discard" "keep"    "discard" "keep"    "keep"   
#[41] "keep"    "keep"    "keep"    "keep"    "keep"    "keep"    "keep"    "keep"   
#[49] "keep"    "discard"

正则表达式dog|cat告诉正则表达式引擎查找"dog"或"cat"，并返回两者的匹配项。

Answer 2

尽可能避免ifelse。例如，这很好用

c("Discard", "Keep")[grepl("(dog|cat)", data$animal) + 1]

对于123种子，您将获得

##  [1] "Keep"    "Keep"    "Discard" "Keep"    "Keep"    "Keep"    "Discard" "Keep"   
##  [9] "Discard" "Discard" "Keep"    "Discard" "Keep"    "Discard" "Keep"    "Keep"   
## [17] "Keep"    "Keep"    "Keep"    "Keep"    "Keep"    "Keep"    "Keep"    "Keep"   
## [25] "Keep"    "Keep"    "Discard" "Discard" "Keep"    "Keep"    "Keep"    "Keep"   
## [33] "Keep"    "Keep"    "Keep"    "Discard" "Keep"    "Keep"    "Keep"    "Keep"   
## [41] "Keep"    "Discard" "Discard" "Keep"    "Keep"    "Keep"    "Keep"    "Discard"
## [49] "Keep"    "Keep"

Answer 3

不确定你尝试了什么，但这似乎有效：

data$keep <- ifelse(grepl(paste(matches, collapse = "|"), data$animal), "Keep","Discard")

与您链接的答案类似。

诀窍是使用粘贴：

paste(matches, collapse = "|")
#[1] "cat|dog"

因此，它会使用dog OR cat创建一个正则表达式，并且还可以使用很长的模式列表，而无需键入每个模式。

编辑：

如果您以后执行此操作，则根据＆＃34; Keep＆＃34;对data.frame进行子集化。和＆＃34;丢弃＆＃34;条目，你可以直接使用：

data[grepl(paste(matches, collapse = "|"), data$animal),]

这样，grepl的结果为TRUE或FALSE用于子集。

在R中grepl以查找与任何字符串列表的匹配

3 个答案:

编辑：