在R中用grepl搜索时转发NA

Question

Is there a way to search with grepl and not overwriting the NAs?

grepl('test', c(NA, 'test','bla',NA))
# [1] FALSE  TRUE FALSE FALSE

I would love to get NA TRUE FALSE NA .

Answer 1

Alternatively, you can use str_detect(string, pattern) from Hadley Wickham's stringr package:

> library(stringr)
> str_detect(c(NA, 'test','bla',NA), 'test')
[1]    NA  TRUE FALSE    NA

Note that the arguments are in reverse order compared to grepl() .

Answer 2

Using grepl , we can try the is.na to get the expected output

as.logical(NA^is.na(v1) * grepl("test", v1))
#[1]    NA  TRUE FALSE    NA

or with ifelse

ifelse(is.na(v1), NA, grepl("test", v1))
#[1]    NA  TRUE FALSE    NA

ifelse(is.na(v2), NA, grepl("test", v2))
#[1]    NA  TRUE FALSE    NA  TRUE

Or with replace

replace(grepl("test", v2), is.na(v2), NA)
#[1]    NA  TRUE FALSE    NA  TRUE

data

v1 <- c(NA, 'test','bla',NA)
v2 <- c(v1, "test run")