Hi guys,
I've to create a variable a in which elements are column names of a database.
For example, I have the following column names of a df:
colnames(df)
"PS_01", "PS_01_mod2", "PS_02", "PS_02_mod2"
I want to create a vector a in which elements are the column names of df ending with mod2, so I want to create this situation
a <- "PS_01_mod2", "PS_02_mod2"
How can I do this in a simple way?
•
written
by
Fede_Santos95 •
3 answers
Hi, a simple grep() command will do this for you, and we can add a regular expression ('regex') to ensure positional specificity:
vector <- c('PS_01', 'PS_01_mod2', 'PS_02', 'PS_02_mod2', 'mod2_mod1')
idx <- grep('mod2$', vector)
vector[idx]
[1] "PS_01_mod2" "PS_02_mod2"
The dollar, $, means that we only want 'mod2' appearing at the end of a line.
Note the difference here, without the dollar:
idx <- grep('mod2', vector)
vector[idx]
[1] "PS_01_mod2" "PS_02_mod2" "mod2_mod1"
Kevin
Look into grep, it's a very useful function in R and UNIX command as well.
a <- grep("_mod2$", colnames(df), value=TRUE)
the dollar sign indicates this pattern should be at the end only.
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