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How do I specify a dynamic position for the start of substring?

Answer 1

+5 A:

you can use sub()

video_data_2$Video_full <- sub("^.*\\.","", video_data_2$Video_full)

kohske 2010-06-09 06:56:32

thanks for your answer. worked like a charm.

analyticsPierce 2010-06-11 05:14:14

Answer 2

+3 A:

an approach using strsplit

video_data_2$Video_full <- sapply(strsplit(video_data_2$Video_full, "\\."),head)[2,]

gd047 2010-06-09 08:19:55

Similar to the first answer provided by @Marek, I received a 'non-character argument' error when I tried this. Any thoughts on what might cause it?

analyticsPierce 2010-06-11 05:19:08

Answer 3

+5 A:

Another way to use strsplit

sapply(strsplit(video_data_2$Video_full, "\\."), "[", 2)

which is shorthand from

sapply(strsplit(video_data_2$Video_full, "\\."), function(x) x[2])

Marek 2010-06-09 08:40:00

+1 I like very much the use of "[". What does it mean? (and where is the explanation in R help?)

gd047 2010-06-09 09:17:25

@gd047 Indexing operator "[" is a function and you can reach its help by `?"["` (or `help("[")`). You could use it as any other function e.g.: `\`[\`(letters,3:5)`, but it's really helpful in cases like question or `do.call` or other places when you must directly provide name of function.

Marek 2010-06-09 09:38:16

thank you for providing this answer. I am not sure why but when I ran this function I got a 'non-character argument' error. Any thoughts on what would cause that?

analyticsPierce 2010-06-11 05:13:38

I suppose `video_data_2$Video_full` is a `factor`. So try `sapply(strsplit(as.character(video_data_2$Video_full), "\\."), "[", 2)`

Marek 2010-06-11 07:41:57

Answer 4

+2 A:

Try stringr

library(stringr)
str_split_fixed(video_data_2$Video_full, "\\.", n = 2)[, 2]

hadley 2010-06-10 14:10:47

This solution is much slower than others. You can see this for 10,000 length vector.

Marek 2010-06-10 15:29:33

Prove it! Plus why worry about speed unless you have to.

hadley 2010-06-10 20:33:54

@hadley, thank you for your answer. I went through your docs for this package and would get a lot of use out of it. However, I was not able to get it to install. I'm using the Rbundle in textmate and tried install.packages("stringr", repos = "http://cran.r-project.org/src/contrib/stringr_0.3.tar.gz", type="source"), the message I got back said the package was unavailable. Sorry if this should be a separate question.

analyticsPierce 2010-06-11 05:27:04

You should only need `install.packages("stringr")`. That path is not a valid repository.

hadley 2010-06-11 14:18:33

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How do I specify a dynamic position for the start of substring?

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