R help - Aug 2009 - problems with strsplit using a split of ' \\\ ' : a regex problem

I have a vector of gene symbols, some of which have multiple aliases. In the
case of an alias, they are separated by ' \\\ '.
Here is a real world example, which would represent one element of my
vector:
Eif4g2 /// Eif4g2-ps1 /// LOC678831

What I would like to do is input the vector into a function and output a
vector with just the first alias of each element (or, if there are no
aliases, just the one symbol).

So I wrote a simple little function to do this:
get.first.id.func <- function(vec, splitter){
  vec.lst <- strsplit(vec, splitter)
  first.func <- function(vec1){vec1[1]}
  vec.out <- sapply(vec.lst, first.func)
  vec.out
}

For a trivial example, this works:
> a <- c("a_b", "c_d")
> get.first.id.func(a, "_")
[1] "a" "c"

I am running into problems, however, with the real world split of ' \\\
'
I'm not even able to construct a sample vector of my own! Here is what I
get:
> a <- c('a \\\ b', 'a \\\ b')
> a
[1] "a \\ b" "a \\ b"
> a <- c('a \\\\ b', 'a \\\\ b')
> a
[1] "a \\\\ b" "a \\\\ b"

I KNOW this is related to R's peculiarities with \ escapes, but I don't
have
the expertise to know how to get around it.

I would be very interested to learn:
1. how to construct a vector such that a == c('a \\\ b', 'a \\\
b')
2. how to properly input my split into my function so that I get the split
desired.

Thanks regex experts!
Mark

------------------------------------------------------------
Mark W. Kimpel MD  ** Neuroinformatics ** Dept. of Psychiatry
Indiana University School of Medicine

15032 Hunter Court, Westfield, IN  46074

(317) 490-5129 Work, & Mobile & VoiceMail

"The real problem is not whether machines think but whether men do."
-- B.
F. Skinner
******************************************************************

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You need a escape before each backslash:

a <- c('a \\\\\\ b', 'a \\\\\\ b')
cat(a, "\n")

You can write in this form:

strsplit(a, " .*\\.* ")



On Thu, Aug 27, 2009 at 10:03 PM, Mark Kimpel <mwkimpel@gmail.com> wrote:
> I have a vector of gene symbols, some of which have multiple aliases. In
> the
> case of an alias, they are separated by ' \\\ '.
> Here is a real world example, which would represent one element of my
> vector:
> Eif4g2 /// Eif4g2-ps1 /// LOC678831
>
> What I would like to do is input the vector into a function and output a
> vector with just the first alias of each element (or, if there are no
> aliases, just the one symbol).
>
> So I wrote a simple little function to do this:
> get.first.id.func <- function(vec, splitter){
>  vec.lst <- strsplit(vec, splitter)
>  first.func <- function(vec1){vec1[1]}
>  vec.out <- sapply(vec.lst, first.func)
>  vec.out
> }
>
> For a trivial example, this works:
> > a <- c("a_b", "c_d")
> > get.first.id.func(a, "_")
> [1] "a" "c"
>
> I am running into problems, however, with the real world split of ' \\\
'
> I'm not even able to construct a sample vector of my own! Here is what
I
> get:
> > a <- c('a \\\ b', 'a \\\ b')
> > a
> [1] "a \\ b" "a \\ b"
> > a <- c('a \\\\ b', 'a \\\\ b')
> > a
> [1] "a \\\\ b" "a \\\\ b"
>
> I KNOW this is related to R's peculiarities with \ escapes, but I
don't
> have
> the expertise to know how to get around it.
>
> I would be very interested to learn:
> 1. how to construct a vector such that a == c('a \\\ b', 'a \\\
b')
> 2. how to properly input my split into my function so that I get the split
> desired.
>
> Thanks regex experts!
> Mark
>
> ------------------------------------------------------------
> Mark W. Kimpel MD  ** Neuroinformatics ** Dept. of Psychiatry
> Indiana University School of Medicine
>
> 15032 Hunter Court, Westfield, IN  46074
>
> (317) 490-5129 Work, & Mobile & VoiceMail
>
> "The real problem is not whether machines think but whether men
do." -- B.
> F. Skinner
> ******************************************************************
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O

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