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I've two vectors:
c('abc', 'asdf', 'werd', 'ffssd')
c('ab', 'd', 'w')
I'd like to vectorize the following for-loop:
for(p in 1 : length(patterns)){
count <- count + str_count(texts, p);
}
I used the following commands but both won't work.
> str_count(texts, patterns)
[1] 1 1 1 0
Warning message:
In stri_count_regex(string, pattern, opts_regex = attr(pattern, :
longer object length is not a multiple of shorter object length
> str_count(texts, t(patterns))
[1] 1 1 1 0
Warning message:
In stri_count_regex(string, pattern, opts_regex = attr(pattern, :
longer object length is not a multiple of shorter object length
I'd want a 2d matrix like this:
| patterns
------+--------
| 1 0 0
texts | 0 1 0
| 0 1 1
| 0 1 0
905
Most of R's functions are vectorized, meaning that the function will operate on all elements of a vector without needing to loop through and act on each element one at a time. This makes writing code more concise, easy to read, and less error prone.
R takes a fair amount of heat from the hacker community because it's kind of slow at looping2. It compensates (somewhat) for this weakness by using vectorized functions! Vectorized functions usually involve a behind-the-scenes loop in a low-level language (C or Fortran), which runs way faster than a pure R loop.
For loops can be slow if you are incorrectly growing objects or you have a very fast interior of the loop and the entire thing can be replaced with a vectorized operation. Otherwise you're probably not losing too much efficiency, as the apply family of functions are performing for loops on the inside, too.
You can use outer. I assume you are using str_count from the stringr package.
library(stringr)
texts <- c('abc', 'asdf', 'werd', 'ffssd')
patterns <- c('ab', 'd', 'w')
matches <- outer(texts, patterns, str_count)
# set dim names
colnames(matches) <- patterns
rownames(matches) <- texts
matches
ab d w
abc 1 0 0
asdf 0 1 0
werd 0 1 1
ffssd 0 1 0
EDIT
# or set names directly within 'outer' as noted by @RichardScriven
outer(setNames(nm = texts), setNames(nm = patterns), str_count)
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