I have two character variables (names of objects) and I want to extract the largest common substring.
a <- c('blahABCfoo', 'blahDEFfoo')
b <- c('XXABC-123', 'XXDEF-123')
I want the following as a result:
[1] "ABC" "DEF"
These vectors as input should give the same result:
a <- c('textABCxx', 'textDEFxx')
b <- c('zzABCblah', 'zzDEFblah')
These examples are representative. The strings contain identifying elements, and the remainder of the text in each vector element is common, but unknown.
Is there a solution, in one of the following places (in order of preference):
Base R
Recommended Packages
Packages available on CRAN
The answer to the supposed-duplicate does not fulfill these requirements.
Here's a CRAN package for that:
library(qualV)
sapply(seq_along(a), function(i)
paste(LCS(strsplit(a[i], '')[[1]], strsplit(b[i], '')[[1]])$LCS,
collapse = ""))
If you dont mind using bioconductor packages, then, You can use Rlibstree
. The installation is pretty straightforward.
source("http://bioconductor.org/biocLite.R")
biocLite("Rlibstree")
Then, you can do:
require(Rlibstree)
ll <- list(a,b)
lapply(data.frame(do.call(rbind, ll), stringsAsFactors=FALSE),
function(x) getLongestCommonSubstring(x))
# $X1
# [1] "ABC"
# $X2
# [1] "DEF"
On a side note: I'm not quite sure if Rlibstree
uses libstree 0.42
or libstree 0.43
. Both libraries are present in the source package. I remember running into a memory leak (and hence an error) on a huge array in perl that was using libstree 0.42
. Just a heads up.
Because I have too many things I don't want to do, I did this instead:
Rgames> for(jj in 1:100) {
+ str2<-sample(letters,100,rep=TRUE)
+ str1<-sample(letters,100,rep=TRUE)
+ longs[jj]<-length(lcstring(str1,str2)[[1]])
+ }
Rgames> table(longs)
longs
2 3 4
59 39 2
Anyone care to do a statistical estimate of the actual distribution of matching strings?
(lcstring
is just a brute-force home-rolled function; the output contains all max strings which is why I only look at the first list element)
来源:https://stackoverflow.com/questions/16196327/find-common-substrings-between-two-character-variables