R - test if first occurrence of string1 is followed by string2

r contains
StanLe picture StanLe · Nov 19, 2013 · Viewed 117k times · Source

I have an R string, with the format

s = `"[some letters and numbers]_[a number]_[more numbers, letters, punctuation, etc, anything]"`

I simply want a way of checking if s contains "_2" in the first position. In other words, after the first _ symbol, is the single number a "2"? How do I do this in R?

I'm assuming I need some complicated regex expresion?

Examples:

39820432_2_349802j_32hfh = TRUE

43lda821_9_428fj_2f = FALSE (notice there is a _2 there, but not in the right spot)

Answer

Julián Urbano picture Julián Urbano · Nov 19, 2013 
> grepl("^[^_]+_1",s)
[1] FALSE
> grepl("^[^_]+_2",s)
[1] TRUE

basically, look for everything at the beginning except _, and then the _2.

+1 to @Ananda_Mahto for suggesting grepl instead of grep.

Related questions

Remove rows with all or some NAs (missing values) in data.frame

I'd like to remove the lines in this data frame that: a) contain NAs across all columns. Below is my example data frame. gene hsap mmul mmus rnor cfam 1 ENSG00000208234 0 NA NA NA NA 2 ENSG00000199674 0 2 2 2 2 3 ENSG00000221622 0 NA NA NA NA 4 …

Read More
Drop data frame columns by name

I have a number of columns that I would like to remove from a data frame. I know that we can delete them individually using something like: df$x <- NULL But I was hoping to do this with …

Read More
Changing column names of a data frame

I have a data frame called "newprice" (see below) and I want to change the column names in my program in R. > newprice Chang. Chang. Chang. 1 100 36 136 2 120 -33 87 3 150 14 164 In fact this is what am doing: names(newprice)[1]<-paste("premium") …

Read More