This is the name of a file that I have on R:
> lst.files[1]
[1] "clt_Amon_CanESM2_rcp45_185001-230012.nc"
What I need to do is capture just the part until the 4th underscore (including), so it would be something like this:
clt_Amon_CanESM2_rcp45_
How can I get this in R?
If you know you always have (at least) four underscores, then you could do something like this:
regmatches(lst, regexec(".*_.*_.*_.*_", lst.files[1]))[[1]]
# [1] "clt_Amon_CanESM2_rcp45_"
If potentially not always four, but no underscores in the second part, you could do something like this:
regmatches(lst, regexec(".*_", lst.files[1]))[[1]]
# [1] "clt_Amon_CanESM2_rcp45_"
This doesn't require any extra package, just base R.
Using the qdap package, you can do the following.
x <- "clt_Amon_CanESM2_rcp45_185001-230012.nc"
library(qdap)
beg2char(x, "_", 4, include = TRUE)
# [1] "clt_Amon_CanESM2_rcp45_"
We can also capture the repeating patterns as a group using sub. We match one more more characters from the beginning (^) of the string that is not an underscore ([^_]+) followed by an underscore (\\_) which is repeated 4 times ({4}), capture that as a group by wrapping with parentheses followed by zero or more characters (.*). We replace it with the capture group (\\1) to get the expected output.
sub('^(([^_]+\\_){4}).*', '\\1', str1)
#[1] "clt_Amon_CanESM2_rcp45_"
str1 <- "clt_Amon_CanESM2_rcp45_185001-230012.nc"