R help - Apr 2020 - how to get all strings in a data frame that start with a particular string

Hello,

Hello,

I have a data frame (tot) with about 2000 columns. How can I extract
from it all strings that start with E14?

I tried this:
e14 <- sapply(tot, function(x) grepl("^E14", x))

but this returns me just TRUE and FALSE vector, how do I get actual
strings that start with E14?

Thanks
Ana

Dear Ana

Would it not be possible to use grep instead of grepl and get the values 
using the value = TRUE parameter?

Michael

On 10/04/2020 17:15, Ana Marija wrote:
> Hello,
> 
> Hello,
> 
> I have a data frame (tot) with about 2000 columns. How can I extract
> from it all strings that start with E14?
> 
> I tried this:
> e14 <- sapply(tot, function(x) grepl("^E14", x))
> 
> but this returns me just TRUE and FALSE vector, how do I get actual
> strings that start with E14?
> 
> Thanks
> Ana
> 
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
> 
-- 
Michael
http://www.dewey.myzen.co.uk/home.html

On 2020-04-10 11:15 -0500, Ana Marija wrote:
> I have a data frame (tot) with about 
> 2000 columns. How can I extract from 
> it all strings that start with E14?
> 
> I tried this:
> e14 <- sapply(tot, function(x) grepl("^E14", x))
> 
> but this returns me just TRUE and 
> FALSE vector, how do I get actual 
> strings that start with E14?
Dear Ana,

perhaps you thought of something along 
the lines of this:

  ncol <- 2000
  nrow <- 3
  line <-
    c("a", "b",
      "some text E14 bla bla some more text",
      "d",
      "E14 ... hey this starts and also ends with E14",
      "E14 something-something",
      "another string")
  tot <-
    as.data.frame(matrix(rep(line,
      times=ncol*nrow),
      ncol=ncol,
      byrow=T))
  
  # Now, tot is a df with some cells
  # containing replicates of line, some
  # cells there are now starting with E14
  # ... so we need to convert it to a
  # character matrix to be able to find
  # the indecies of the cells starting
  # with E14:
  
  tot <- as.matrix(tot)
  idx <- grepl("^E14", tot)
  tot[idx]

Best,
Rasmus

Thank you so much!

On Fri, Apr 10, 2020 at 12:00 PM Rasmus Liland <jensrasmus at gmail.com>
wrote:
>
> On 2020-04-10 11:15 -0500, Ana Marija wrote:
> > I have a data frame (tot) with about
> > 2000 columns. How can I extract from
> > it all strings that start with E14?
> >
> > I tried this:
> > e14 <- sapply(tot, function(x) grepl("^E14", x))
> >
> > but this returns me just TRUE and
> > FALSE vector, how do I get actual
> > strings that start with E14?
>
> Dear Ana,
>
> perhaps you thought of something along
> the lines of this:
>
>   ncol <- 2000
>   nrow <- 3
>   line <-
>     c("a", "b",
>       "some text E14 bla bla some more text",
>       "d",
>       "E14 ... hey this starts and also ends with E14",
>       "E14 something-something",
>       "another string")
>   tot <-
>     as.data.frame(matrix(rep(line,
>       times=ncol*nrow),
>       ncol=ncol,
>       byrow=T))
>
>   # Now, tot is a df with some cells
>   # containing replicates of line, some
>   # cells there are now starting with E14
>   # ... so we need to convert it to a
>   # character matrix to be able to find
>   # the indecies of the cells starting
>   # with E14:
>
>   tot <- as.matrix(tot)
>   idx <- grepl("^E14", tot)
>   tot[idx]
>
> Best,
> Rasmus