grepvec

• Finding needles in haystacks
• Install
  • Dependencies
• Examples
• Development
• Use Cases

Finding needles in haystacks

Use grepvec to find needles in haystacks.

That is, search for each item in a vector of patterns (either regular expressions or fixed strings) across each item in a vector of strings.
R’s native ‘grep’ functions search for a single pattern in a vector of strings. To search for many possible patterns across a string or vector of strings, some form of looping is required. grepvec implements this in C so that it is more efficient than native R solutions.

Install

Since this package is not currently on CRAN, you can install it in R with remotes::install_github("hans-elliott99/grepvec").

For development you can, clone the repo and use devtools::load_all or devtools::install.

Dependencies

You have nothing else to install…

I hope to keep grepvec lightweight, and there are no package dependencies other than the “base” R packages (utils and base specifically), so you don’t need to install anything else.

For development, testthat is needed for unit testing, and I use devtools (and its dependencies) as well.

Examples

Please see examples/grepvec.md for more examples.

library(grepvec)

grepvec(needles = c("some", "other", "string"),
        haystacks = c("some string 1", "another string"))

[[1]]
[1] 1 3

[[2]]
[1] 2 3

grepvec(c("^h", ".ell.", "ello$"), c("hello", "jelly"))

[[1]]
[1] 1 2 3

[[2]]
[1] 2

grepvec(c("^h", ".ell.", "ello$"), c("hello", "jelly"),
        value = TRUE)

[[1]]
[1] "^h"    ".ell." "ello$"

[[2]]
[1] ".ell."

grepvec(c("one", "possib", "many"),
        c("Some text which might possibly contain one of many keywords",
          "Another string, without many words",
          "A third impossibly boring string",
          "I'm done thinking of strings."),
        out = "haystacks",
        value = TRUE)

[[1]]
[1] "Some text which might possibly contain one of many keywords"
[2] "I'm done thinking of strings."                              

[[2]]
[1] "Some text which might possibly contain one of many keywords"
[2] "A third impossibly boring string"                           

[[3]]
[1] "Some text which might possibly contain one of many keywords"
[2] "Another string, without many words"                         

grepvec(letters, paste(letters, collapse = ""), value = TRUE)

[[1]]
 [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m" "n" "o" "p" "q" "r" "s"
[20] "t" "u" "v" "w" "x" "y" "z"

grepvec(letters, paste(letters, collapse = ""), matchrule = "first", value = TRUE)

[[1]]
[1] "a"

grepvec(letters, paste(letters, collapse = ""), matchrule = "last", value = TRUE)

[[1]]
[1] "z"

x <- grepvec(letters[1:6], c("abc", "123"), out = "object")
setNames(grepvec::by_hay(x, value = TRUE), x$haystacks)

$abc
[1] "a" "b" "c"

$`123`
character(0)

setNames(grepvec::by_ndl(x, value = TRUE), x$needles)

$a
[1] "abc"

$b
[1] "abc"

$c
[1] "abc"

$d
character(0)

$e
character(0)

$f
character(0)

Development

I have used grepvec in my own work but it lacks testing by other users. If you find it useful please let me know, or let me know how I might improve it to better suit your needs.

Feel free to contribute by creating issues or submitting pull requests.

Thanks!

Use Cases

The grepvec function provides a convenient way to search a vector of strings (haystacks) for multiple patterns (needles) at once, which is not directly supported by base R functions like grep, or by similair stringr functions.

While it’s possible to combine multiple patterns into a single regular expression using the “|” operator, this can be difficult to manage for a large number of patterns. Further, it doesn’t easily allow you to identify which specific patterns were matched, or how many.

Some potential use cases:

• Text Analysis: If you’re analyzing a corpus of text (like a collection of documents, tweets, or web pages), you might want to find occurrences of a list of specific key words or phrases. grepvec can be used to efficiently perform this task.

• Data Cleaning: When cleaning data, you often need to find and replace certain patterns. If you have a list of known errors or inconsistencies (like misspellings or alternative representations of the same value), you can use grepvec to identify these in your data.

• Others?