[R] Parsing

[jim holtman]

This should do what you want: (it uses loops; you can work at
replacing those with 'lapply' and such -- it all depends on if it is
going to take you more time to rewrite the code than to process a set
of data; you never did say how large the data was).  This also "grows"
a data.frame, but you have not indicated how efficient is has to be.
So this could be used as a model.

> x <- readLines(textConnection("x      x_string
+ y      y_string
+ id1    id1_string
+ id2    id2_string
+ z      z_string
+ w      w_string
+ stuff  stuff  stuff
+ stuff  stuff  stuff
+ stuff  stuff  stuff
+ //
+ x      x_string1
+ y      y_string1
+ z      z_string1
+ w      w_string1
+ stuff  stuff  stuff
+ stuff  stuff  stuff
+ stuff  stuff  stuff
+ //
+ x      x_string2
+ y      y_string2
+ id1    id1_string1
+ id2    id2_string1
+ z      z_string2
+ w      w_string2
+ stuff  stuff  stuff
+ stuff  stuff  stuff
+ stuff  stuff  stuff
+ //"))
> # I assume that each group is delimited by "//"
> # initialize data.frame with desired values
> .keys <- data.frame(x=NA, y=NA, id1=NA, id2=NA, w=NA)
> .out <- .keys  # for the first pass
> .save <- NULL
> for (i in seq_along(x)){
+     if (x[i] == "//"){  # output the current data
+         .save <- rbind(.save, .out)
+         .out <- .keys    # setup for the next pass
+     } else {
+         .split <- strsplit(x[i], "\\s+")
+         if (.split[[1]][1] %in% names(.out)){
+             .out[[.split[[1]][1]]] <- .split[[1]][2]
+         }
+     }
+ }
> .save
          x         y         id1         id2         w
1  x_string  y_string  id1_string  id2_string  w_string
2 x_string1 y_string1        <NA>        <NA> w_string1
3 x_string2 y_string2 id1_string1 id2_string1 w_string2


On Wed, Jul 9, 2008 at 5:33 AM, Paolo Sonego <paolo.sonego at gmail.com> wrote:
> Dear R users,
>
> I have a big text file formatted like this:
>
> x      x_string
> y      y_string
> id1    id1_string
> id2    id2_string
> z      z_string
> w      w_string
> stuff  stuff  stuff
> stuff  stuff  stuff
> stuff  stuff  stuff
> //
> x      x_string1
> y      y_string1
> z      z_string1
> w      w_string1
> stuff  stuff  stuff
> stuff  stuff  stuff
> stuff  stuff  stuff
> //
> x      x_string2
> y      y_string2
> id1    id1_string1
> id2    id2_string1
> z      z_string2
> w      w_string2
> stuff  stuff  stuff
> stuff  stuff  stuff
> stuff  stuff  stuff
> //
> ...
> ...
>
>
> I'd like to parse this file and retrieve the x, y, id1, id2, z, w fields and
> save them into a a matrix object:
>
> x        y          id1         id2         z          w
> x_string y_string   id1_string  id2_string  z_string   w_string  x_string1
> y_string1 NA          NA          z_string1  w_string1
> x_string2 y_string2 id1_string1 id2_string1 z_string2  w_string2
> ...
> ...
>
> id1, id2 fields  are not always present within a section (the interval
> between x and the last stuff) and
> I'd like to insert a NA when they are absent (see above) so that
> length(x)==length(y)==length(id1)==... .
>
> Without the id1, id2 fields the task is easily solvable  importing the text
> file with readLines and retrieving the single fields with grep:
>
> input = readLines("file.txt")
> x = grep("^x\\s", input, value = T)
> id1 = grep("^id1\\s", input, value = T)
> ...
>
> I'd like to accomplish this task entirely in R (no SQL, no perl script),
>  possibly without using loops.
>
> Any suggestions are quite welcome!
>
> Regards,
> Paolo
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?