Fast partial string matching in R

Question

Given a vector of strings texts and a vector of patterns patterns, I want to find any matching pattern for each text.

For small datasets, t

Answer 1

Have you accurately characterized your problem and the performance you're seeing? Here are the Complete Works of William Shakespeare and a query against them

text = readLines("~/Downloads/pg100.txt")
pattern <- 
    strsplit("all the world's a stage and all the people players", " ")[[1]]

which seems to be much more performant than you imply?

> length(text)
[1] 124787
> system.time(xx <- lapply(pattern, grepl, text, fixed=TRUE))
   user  system elapsed 
  0.444   0.001   0.444 
## avoid retaining memory; 500 x 500 case; no blank lines
> text = text[nzchar(text)]
> system.time({ for (p in rep(pattern, 50)) grepl(p, text[1:500], fixed=TRUE) })
   user  system elapsed 
  0.096   0.000   0.095 

We're expecting linear scaling with both the length (number of elements) of pattern and text. It seems I mis-remember my Shakespeare

> idx = Reduce("+", lapply(pattern, grepl, text, fixed=TRUE))
> range(idx)
[1] 0 7
> sum(idx == 7)
[1] 8
> text[idx == 7]
[1] "    And all the men and women merely players;"                       
[2] "    cicatrices to show the people when he shall stand for his place."
[3] "    Scandal'd the suppliants for the people, call'd them"            
[4] "    all power from the people, and to pluck from them their tribunes"
[5] "    the fashion, and so berattle the common stages (so they call"    
[6] "    Which God shall guard; and put the world's whole strength"       
[7] "    Of all his people and freeze up their zeal,"                     
[8] "    the world's end after my name-call them all Pandars; let all"