[R] Partition vector of strings into lines of preferred width

[Martin Morgan]

> strwrap(text)
[1] "What is the best way to split/cut a vector of strings into lines of"
[2] "preferred width? I have come up with a simple solution, albeit naive,"
[3] "as it involves many arithmetic divisions. I have an alternative idea"
[4] "which avoids this problem. But I may miss some existing functionality!"

Maybe used as

> strwrap(text)  |> paste(collapse = "\n") |> cat("\n")
What is the best way to split/cut a vector of strings into lines of
preferred width? I have come up with a simple solution, albeit naive,
as it involves many arithmetic divisions. I have an alternative idea
which avoids this problem. But I may miss some existing functionality!
>

?

From: R-help <r-help-bounces using r-project.org> on behalf of Leonard Mada via R-help <r-help using r-project.org>
Date: Friday, October 28, 2022 at 5:42 PM
To: R-help Mailing List <r-help using r-project.org>
Subject: [R] Partition vector of strings into lines of preferred width
Dear R-Users,

text = "
What is the best way to split/cut a vector of strings into lines of
preferred width?
I have come up with a simple solution, albeit naive, as it involves many
arithmetic divisions.
I have an alternative idea which avoids this problem.
But I may miss some existing functionality!"

# Long vector of strings:
str = strsplit(text, " |(?<=\n)", perl=TRUE)[[1]];
lenWords = nchar(str);

# simple, but naive solution:
# - it involves many divisions;
cut.character.int = function(n, w) {
     ncm = cumsum(n);
     nwd = ncm %/% w;
     count = rle(nwd)$lengths;
     pos = cumsum(count);
     posS = pos[ - length(pos)] + 1;
     posS = c(1, posS);
     pos = rbind(posS, pos);
     return(pos);
}

npos = cut.character.int(lenWords, w=30);
# lets print the results;
for(id in seq(ncol(npos))) {
    len = npos[2, id] - npos[1, id];
    cat(str[seq(npos[1, id], npos[2, id])], c(rep(" ", len), "\n"));
}


The first solution performs an arithmetic division on all string
lengths. It is possible to find out the total length and divide only the
last element of the cumsum. Something like this should work (although it
is not properly tested).


w = 30;
cumlen = cumsum(lenWords);
max = tail(cumlen, 1) %/% w + 1;
pos = cut(cumlen, seq(0, max) * w);
count = rle(as.numeric(pos))$lengths;
# everything else is the same;
pos = cumsum(count);
posS = pos[ - length(pos)] + 1;
posS = c(1, posS);
pos = rbind(posS, pos);

npos = pos; # then print


The cut() may be optimized as well, as the cumsum is sorted ascending. I
did not evaluate the efficiency of the code either.

But do I miss some existing functionality?


Note:

- technically, the cut() function should probably return a vector of
indices (something like: rep(seq_along(count), count)), but it was more
practical to have both the start and end positions.


Many thanks,


Leonard

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