I have been using stringr since it’s supposed to be faster, but I found out today that it’s much slower when dealing with factor terms. I didn’t see any warning that this would be the case nor why it is.

For example:

string_options = c("OneWord", "TwoWords", "ThreeWords")

sample_chars = sample(string_options, 1e6, replace = TRUE)
sample_facts = as_factor(sample_chars)

When working with character terms, base R is slower than stringr, as expected. But when dealing with factor terms, base R is like 30x faster.

bench::mark(
    base_chars = grepl("Two", sample_chars),
    stringr_chars = str_detect(sample_chars, "Two"),
    base_facts = grepl("Two", sample_facts),
    stringr_facts = str_detect(sample_facts, "Two")
)

# A tibble: 4 × 13
#  expression         min   median `itr/sec` mem_alloc `gc/sec` n_itr  n_gc total_time result            memory             time             gc      
#  <bch:expr>    <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl> <int> <dbl>   <bch:tm> <list>            <list>             <list>           <list>  
#1 base_chars     116.1ms 116.38ms      8.58    3.81MB        0     5     0      583ms <lgl [1,000,000]> <Rprofmem [1 × 3]> <bench_tm [5]>   <tibble>
#2 stringr_chars  86.04ms   88.2ms     11.3     3.81MB        0     6     0      532ms <lgl [1,000,000]> <Rprofmem [2 × 3]> <bench_tm [6]>   <tibble>
#3 base_facts      3.59ms   3.65ms    271.     11.44MB        0   136     0      501ms <lgl [1,000,000]> <Rprofmem [3 × 3]> <bench_tm [136]> <tibble>
#4 stringr_facts  90.71ms  91.29ms     10.9    11.44MB        0     6     0      549ms <lgl [1,000,000]> <Rprofmem [3 × 3]> <bench_tm [6]>   <tibble>

It looks like stringr isn’t doing anything different with factor terms but base R is significantly optimizing it. Is this expected behaviour? Should I report this as a stringr issue? Is there some stringr setting I’m completely missing? I’d like to not have to think about the format of the data to determine if I’m using stringr or base R.