Checking if a vector starts with a number

Question

I have a pretty straight forward question. Sorry if this has already been asked somewhere, but I could not find the answer... I want to check if genenames start with a number, and if they do start with a number, I want to add 'aaa_' to the genename. Therefor I used the following code:

geneName <- "2310067B10Rik"
if (is.numeric(substring(geneName, 1, 1))) {
  geneName <<- paste("aaaa_", geneName, sep="")
}

What I want to get back is aaaa_2310067B10Rik. However, is.numeric returns a FALSE, because the substring gives "2" in quotations as a character. I've also tries to use noquote(), but that didnt work, and as.numeric() around the substring, but then it also applies the if code to genes that don't start with a number. Any suggestions? Thanks!

explore the result of `is.na(as.numeric(substring(geneName, 1, 1)))` or https://stackoverflow.com/questions/4736/learning-regular-expressions and use `grepl()`, i.e. `grepl("^\\d", geneName)` — jogo, Aug 17 '18 at 08:51
`<<-` is dangerous! `library("fortunes"); fortune(174)` read https://www.burns-stat.com/pages/Tutor/R_inferno.pdf Circle 6 — jogo, Aug 17 '18 at 08:56

jogo · Answer 1 · 2018-08-17T09:32:56.157

4

Here is a solution with regex (Learning Regular Expressions ):

geneName <- c("2310067B10Rik", "Z310067B10Rik")
sub("^(\\d)", "aaa_\\1", geneName)

or as PERL-flavoured variant (thx to @snoram):

sub("^(?=\\d)", "aaa_", geneName, perl = TRUE)

edited Aug 17 '18 at 09:32

answered Aug 17 '18 at 09:07

jogo

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Similarly flavoured alternative `sub("^(?=\\d)", "aaa_", geneName, perl = TRUE)`. +1 btw. – s_baldur Aug 17 '18 at 09:28

score 1 · Answer 2 · answered Aug 17 '18 at 09:00

1

Using the replace() function:

start_nr <- grep("^\\d", geneName)
replace(geneName, start_nr, paste0("aaaa_", geneName[start_nr]))
[1] "aaaa_2310067B10Rik" "foo"                "aaaa_9bar"

Where:

geneName <- c("2310067B10Rik", "foo", "9bar")

answered Aug 17 '18 at 09:00

s_baldur

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Lennyy · Accepted Answer · 2018-08-17T08:59:49.703

0

geneName <- c("2310067B10Rik", "foo") 

ifelse(substring(geneName, 1,1) %in% c(0:9), paste0("aaaa_", geneName), geneName)

[1] "aaaa_2310067B10Rik" "foo"

Or based on above comment, you could replace substring(geneName, 1,1) %in% c(0:9) by grepl("^\\d", geneName)

edited Aug 17 '18 at 08:59

answered Aug 17 '18 at 08:53

Lennyy

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Your welcome. Please consider to upvote or accept the answer if it was helpful to you. Also see: https://stackoverflow.com/help/someone-answers – Lennyy Aug 17 '18 at 11:24

score 0 · Answer 4 · answered Aug 17 '18 at 09:01

Using regex:

You can first check the first character of your geneName and if it is digit then you can append as follow:

geneName <- "2310067B10Rik"
ifelse(grepl("^[0-9]*$", substring(geneName, 1,1)),paste("aaaa",geneName,sep="_"),)

Output:

[1] "aaaa_2310067B10Rik"

score 0 · Answer 5 · answered Aug 17 '18 at 09:07

0

 geneName=function(x){
   if( grepl("^[0-9]",x) ){
     as.character(glue::glue('aaaa_{x}'))
   }else{x}
 }
> geneName("2310067B10Rik")
[1] "aaaa_2310067B10Rik"
> geneName("sdsad")
[1] "sdsad"

answered Aug 17 '18 at 09:07

jyjek

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While this code may answer the question, providing additional context regarding how and/or why it solves the problem would improve the answer's long-term value. – Nic3500 Aug 17 '18 at 12:41
@Nic3500 totaly agree – jyjek Aug 17 '18 at 12:43

Checking if a vector starts with a number

5 Answers5