R help - Feb 2009 - how to delete specific rows in a data frame where the first column matches any string from a list

Hi,

I'm new in the mailing list but I would appreciate if you could help
me with this:
I have a big matrix from where I need to delete specific rows. The
second entry on these rows to delete should match any string within a
list (other file with just one column).
Thank you so much!

Laura

Laura:

When posting to this list, it is best to provide a small example. This
will facilitate better help. Here is an example of what you want to do.
> mat <- matrix(rnorm(10), ncol=2)
> mat
           [,1]       [,2]
[1,] -0.1418628 -1.4559344
[2,]  0.4022863  1.4727494
[3,]  0.0158310  0.3471318
[4,]  0.3962089 -0.5179074
[5,]  1.8098082  0.7238309

### Remove rows 2 and 3
> (newMat <- mat[c(-2,-3),])
           [,1]       [,2]
[1,] -0.1418628 -1.4559344
[2,]  0.3962089 -0.5179074
[3,]  1.8098082  0.7238309 

I don't know what you mean about the second part (match a string on a
list). So, I didn't do anything with that
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Laura 
> Rodriguez Murillo
> Sent: Friday, February 06, 2009 10:26 AM
> To: r-help at r-project.org
> Subject: [R] how to delete specific rows in a data frame 
> where the firstcolumn matches any string from a list
> 
> Hi,
> 
> I'm new in the mailing list but I would appreciate if you 
> could help me with this:
> I have a big matrix from where I need to delete specific 
> rows. The second entry on these rows to delete should match 
> any string within a list (other file with just one column).
> Thank you so much!
> 
> Laura
> 
> ______________________________________________
> R-help at 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.
>

Laura Rodriguez Murillo wrote:
> Hi,
>
> I'm new in the mailing list but I would appreciate if you could help
> me with this:
> I have a big matrix from where I need to delete specific rows. The
> second entry on these rows to delete should match any string within a
> list (other file with just one column).
> Thank you so much!
>
>   
here's one way to do it, illustrated with dummy data:

# dummy character matrix
data = matrix(replicate(20, paste(sample(letters, 20), collapse="")),
ncol=2)

# filter out rows where second column does not match 'a'
data[-grep('a', d[,2]),]

this will work also if your data is actually a data frame:

data = as.data.frame(data)
data[-grep('a', d[,2]),]

note, due to a known issue with grep, this won't work correctly if there
are *no* rows that do *not* match the pattern:

data[-grep('1', d[,2]),]
# should return all of data, but returns an empty matrix

with the upcoming version of r, grep will have an additional argument
which will make this problem easy to fix:

data[grep('a', d[,2], invert=TRUE),]


vQ

Thank you so much! I finally got it.

Laura

2009/2/6 Sebastien Bihorel <Sebastien.Bihorel at
cognigencorp.com>:
> Hi Laura,
>
> You might want to read the manual on Data importation and exportation on
the
> cran webpage http://cran.r-project.org/
> Otherwise, have a look at ?read.table.
>
> Sebastien
>