# [R] matching country name tables from different sources

Gabor Grothendieck ggrothendieck at gmail.com
Tue Jan 10 17:29:03 CET 2006

```If they were the same you could use merge.   To figure out
the correspondence automatically or semiautomatically, try this:

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 <pensterfuzzer at yahoo.de> 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?
>
>
>  All the best,
>    Werner
>
>
>
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