Find if multiple characters in a string

Question

I have a string like this

fileName <- 'tyi_myRef_2019_2020'

I want to check if any of the following characters are present in the fileName and if yes, assign it to an object.

myChar <- c('myPer','myRef','myYe','myQr')

The way I did this is:

if(grepl('myPer', fileName)) {myObject <- 'myPer'}
if(grepl('myRef', fileName)) {myObject <- 'myRef'}
if(grepl('myYe', fileName)) {myObject <- 'myYe'}
if(grepl('myQr', fileName)) {myObject <- 'myQr'}

myObject
"myRef"

Is there a shorter way to do this?

relevant - possible duplicate: https://stackoverflow.com/questions/26319567/use-grepl-to-search-either-of-multiple-substrings-in-a-text — Sotos, Jul 24 '19 at 14:59

GKi · Answer 1 · 2019-08-19T07:46:39.357

2

You can use sapply like:

myObject <- myChar[sapply(myChar, function(x) {grepl(x, fileName)})]
myObject
#[1] "myRef"

or even shorter as @g-grothendieck suggested:

myObject <- myChar[sapply(myChar, grepl, fileName)]

In case you have more than one hit myObject will hold all hits, what is not the case with your if statements, which will overwrite. With myObject[length(myObject)] you will get the last hit like you do with the if's.

You can also use | in the regex and get the match like:

myObject <- sub(paste0(".*(", paste(myChar, collapse="|"), ").*"), "\\1", fileName)

edited Aug 19 '19 at 07:46

answered Jul 24 '19 at 14:58

GKi

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@G.Grothendieck Thanks! I have included your suggestion in the answer. Is this OK? – GKi Jul 24 '19 at 15:06

akrun · Answer 2 · 2019-07-24T15:01:34.563

An option is to paste them into a single string collapse by | and feed that as pattern in grepl. The | will act as OR to check if any of the substrings are present in the 'fileName'

grepl(paste(myChar, collapse="|"), fileName)

Or another option is to extract

library(stringr)
str_extract(fileName, paste(myChar, collapse = "|"))
#[1] "myRef"

If wee need to assign, then

myChar[lengths(sapply(myChar, function(x) grep(x, fileName))) > 0]
#[1] "myRef"

score 1 · Answer 3 · answered Jul 24 '19 at 15:00

1

With stringr:

 res<-stringr::str_extract_all(fileName,myChar)
   res[lengths(res)>0]
[[1]]
[1] "myRef"

With base:

res<-Map(function(x,y) x[grep(x,y)],myChar,fileName)
res[lengths(res)>0]
$myRef
[1] "myRef"

answered Jul 24 '19 at 15:00

NelsonGon

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Find if multiple characters in a string

3 Answers3