[R] matching country name tables from different sources
Gabor Grothendieck
ggrothendieck at gmail.com
Tue Jan 10 20:43:43 CET 2006
You can improve it somewhat by first accepting all the largest
matches and removing the rows and columns for those and
repeatedly doing that with what is left.
On 1/10/06, Werner Wernersen <pensterfuzzer at yahoo.de> wrote:
> Thanks for the nice code, Gabor!
>
> Unfortunately, it seems not to work for my purpose, confuses lots of
> countries when I compare two lists of over 150 countries each.
> Do you have any other suggestions?
>
>
>
> Gabor Grothendieck <ggrothendieck at gmail.com> schrieb:
> If they were the same you could use merge. To figure out
> the correspondence automatically or semiautomatically, try this:
>
> x <- c("Canada", "US", "Mexico")
> y <- c("Kanada", "United States", "Mehico")
> result <- outer(x, y, function(x,y) mapply(lcs2, x, y))
> result[] <- sapply(result, nchar)
> # try both which.max and which.min and if you are lucky
> # one of them will give unique values and that is the one to use
> # In this case which.max does.
> apply(result, 1, which.max) # 1 2 3
>
> # calculate longest common subsequence between 2 strings
> lcs2 <- function(s1,s2) {
> longest <- function(x,y) if (nchar(x) > nchar(y)) x else y
> # Make sure args are strings
> a <- as.character(s1); an <- nchar(s1)+1
> b <- as.character(s2); bn <- nchar(s2)+1
>
>
> # If one arg is an empty string, returns the length of the other
> if (nchar(a)==0) return(nchar(b))
> if (nchar(b)==0) return(nchar(a))
>
>
> # Initialize matrix for calculations
> m <- matrix("", nrow=an, ncol=bn)
>
> for (i in 2:an)
> for (j in 2:bn)
> m[i,j] <- if (substr(a,i-1,i-1)==substr(b,j-1,j-1))
> paste(m[i-1,j-1], substr(a,i-1,i-1), sep = "")
> else
> longest(m[i-1,j], m[i,j-1])
>
> # Returns the distance
> m[an,bn]
> }
>
>
>
> On 1/10/06, Werner Wernersen wrote:
> > Hi,
> >
> > Before I reinvent the wheel I wanted to kindly ask you for your opinion if
> there is a simple way to do it.
> >
> > I want to merge a larger number of tables from different data sources in R
> and the matching criterium are country names. The tables are of different
> size and sometimes the country names do differ slightly.
> >
> > Has anyone done this or any recommendation on what commands I should look
> at to automize this task as much as possible?
> >
> > Thanks a lot for your effort in advance.
> >
> > All the best,
> > Werner
> >
> >
> >
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>
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