merge data with partial match in r

Question

I have two datasets

datf1 <- data.frame (name = c("regular", "kklmin", "notSo", "Jijoh",
 "Kish", "Lissp", "Kcn", "CCCa"),
 number1 = c(1, 8, 9,  2,  18, 25, 33,   8))
#-----------
    name number1
1 regular       1
2  kklmin       8
3   notSo       9
4   Jijoh       2
5    Kish      18
6   Lissp      25
7     Kcn      33
8    CCCa       8

 datf2 <- data.frame (name = c("reGulr", "ntSo", "Jijoh", "sean", "LiSsp",
 "KcN", "CaPN"),
   number2 = c(2, 8, 12,    13, 20, 18,   13))
#-------------
   name number2
1 reGulr       2
2   ntSo       8
3  Jijoh      12
4   sean      13
5  LiSsp      20
6    KcN      18
7   CaPN      13

I want to merge them by name column, however with partial match is allowed (to avoid hampering merging spelling errors in large data set and even to detect such spelling errors) and for example

(1) If consecutive four letters (all if the number of letters are less than 4) at any position - match that is fine

 ABBCD = BBCDK = aBBCD = ramABBBCD = ABB 

(2) Case sensitivity is off in the match e.g ABBCD = aBbCd

(3) The new dataset will have both names (names from datf1 and datf2) preserved. So that letter we can detect if the match is perfect (may a separate column with how many letter do match)

Is such merge possible ?

Edits:

datf1 <- data.frame (name = c("xxregular", "kklmin", "notSo", "Jijoh",
             "Kish", "Lissp", "Kcn", "CCCa"),
                     number1 = c(1, 8, 9,  2,  18, 25, 33,   8))
datf2 <- data.frame (name = c("reGulr", "ntSo", "Jijoh", "sean", 
             "LiSsp", "KcN", "CaPN"),
                     number2 = c(2, 8, 12,  13, 20, 18,   13))


uglyMerge(datf1, datf2)
       name1  name2 number1 number2 matches
1  xxregular   <NA>       1      NA       0
2     kklmin   <NA>       8      NA       0
3      notSo   <NA>       9      NA       0
4      Jijoh  Jijoh       2      12       5
5       Kish   <NA>      18      NA       0
6      Lissp  LiSsp      25      20       5
7        Kcn    KcN      33      18       3
8       CCCa   <NA>       8      NA       0
9       <NA> reGulr      NA       2       0
10      <NA>   ntSo      NA       8       0
11      <NA>   sean      NA      13       0
12      <NA>   CaPN      NA      13       0

Answer 1

Maybe there is a simple solution but I can't find any.
IMHO you have to implement this kind of merging for your own.
Please find an ugly example below (there is a lot of space for improvements):

uglyMerge <- function(df1, df2) {

    ## lower all strings to allow case-insensitive comparison
    lowerNames1 <- tolower(df1[, 1]);
    lowerNames2 <- tolower(df2[, 1]);

    ## split strings into single characters
    names1 <- strsplit(lowerNames1, "");
    names2 <- strsplit(lowerNames2, "");

    ## create the final dataframe
    mergedDf <- data.frame(name1=as.character(df1[,1]), name2=NA, 
                        number1=df1[,2], number2=NA, matches=0,
                        stringsAsFactors=FALSE);

    ## store names of dataframe2 (to remember which strings have no match)
    toMerge <- df2[, 1];

    for (i in seq(along=names1)) {
        for (j in seq(along=names2)) {
            ## set minimal match to 4 or to string length
            minMatch <- min(4, length(names2[[j]]));

            ## find single matches
            matches <- names1[[i]] %in% names2[[j]];

            ## look for consecutive matches
            r <- rle(matches);

            ## any matches found?
            if (any(r$values)) {
                ## find max consecutive match
                possibleMatch <- r$value == TRUE;
                maxPos <- which(which.max(r$length[possibleMatch]) & possibleMatch)[1];

                ## store max conscutive match length
                maxMatch <- r$length[maxPos];

                ## to remove FALSE-POSITIVES (e.g. CCC and kcn) find 
                ## largest substring
                start <- sum(r$length[0:(maxPos-1)]) + 1;
                stop <- start + r$length[maxPos] - 1;
                maxSubStr <- substr(lowerNames1[i], start, stop);

                ## all matching criteria fulfilled
                isConsecutiveMatch <- maxMatch >= minMatch &&
                                    grepl(pattern=maxSubStr, x=lowerNames2[j], fixed=TRUE) &&
                                    nchar(maxSubStr) > 0;

                if (isConsecutiveMatch) {
                    ## merging
                    mergedDf[i, "matches"] <- maxMatch
                    mergedDf[i, "name2"] <- as.character(df2[j, 1]);
                    mergedDf[i, "number2"] <- df2[j, 2];

                    ## don't append this row to mergedDf because already merged
                    toMerge[j] <- NA;

                    ## stop inner for loop here to avoid possible second match
                    break;
                }
            }
        } 
    }

    ## append not matched rows to mergedDf
    toMerge <- which(df2[, 1] == toMerge);
    df2 <- data.frame(name1=NA, name2=as.character(df2[toMerge, 1]), 
                    number1=NA, number2=df2[toMerge, 2], matches=0, 
                    stringsAsFactors=FALSE);
    mergedDf <- rbind(mergedDf, df2);

    return (mergedDf);
}

Output:

> uglyMerge(datf1, datf2)
    name1  name2 number1 number2 matches
1  xxregular reGulr       1       2       5
2     kklmin   <NA>       8      NA       0
3      notSo   <NA>       9      NA       0
4      Jijoh  Jijoh       2      12       5
5       Kish   <NA>      18      NA       0
6      Lissp  LiSsp      25      20       5
7        Kcn    KcN      33      18       3
8       CCCa   <NA>       8      NA       0
9       <NA>   ntSo      NA       8       0
10      <NA>   sean      NA      13       0
11      <NA>   CaPN      NA      13       0

Answer 2

agrep will get you started.

something like:

lapply(tolower(datf1$name), function(x) agrep(x, tolower(datf2$name)))

then you can adjust the max.distance parameter until you get the appropriate amount of matching. then merge however you like.