r - merging two files into a new file

Question

I have 2 files with say 3 columns and a few rows.

1    2    10
2    3    20
3    4    30
4    5    40
5    1    50
6    1    60

and

1    8    10
2    3    100
3    4    45
4    5    78
5    2    99
6    80   60

Now i want to create a third file having all the values of first two files and also if first and second column of both the files are same then in third file the values corresponding to them should like say,value in third column of first file must be in third column of newly created file and value in third column of second file must be in fourth column of newly created file. According to above example answer should be

1  2  10  0
2  3  20  100
3  4  30  45
4  5  40  78
1  8  10   0
5  1  50   0
6  1  60   0
5  2  99   0
6  80 60   0

Answer 1

 res <- merge(dat1,dat2, by=c("V1", "V2"),all=TRUE)
 indx <- is.na(res[,3]) 
 res[indx,3] <- res[indx,4]
 res[indx,4] <- NA
 res[is.na(res)] <- 0
 #    V1 V2 V3.x V3.y
 #1  1  2   10    0
 #2  1  8   10    0
 #3  2  3   20  100
 #4  3  4   30   45
 #5  4  5   40   78
 #6  5  1   50    0
 #7  5  2   99    0
 #8  6  1   60    0
 #9  6 80   60    0

data

 dat1 <- structure(list(V1 = structure(1:6, .Label = c("1", "2", "3", 
 "4", "5", "6"), class = "factor"), V2 = structure(c(2L, 3L, 4L, 
 5L, 1L, 1L), .Label = c("1", "2", "3", "4", "5"), class = "factor"), 
V3 = structure(1:6, .Label = c("10", "20", "30", "40", "50", 
"60"), class = "factor")), .Names = c("V1", "V2", "V3"), class = "data.frame", row.names = c(NA, 
-6L))

 dat2 <- structure(list(V1 = structure(1:6, .Label = c("1", "2", "3", 
 "4", "5", "6"), class = "factor"), V2 = structure(c(5L, 2L, 3L, 
 4L, 1L, 6L), .Label = c("2", "3", "4", "5", "8", "80"), class = "factor"), 
V3 = structure(c(1L, 2L, 3L, 5L, 6L, 4L), .Label = c("10", 
"100", "45", "60", "78", "99"), class = "factor")), .Names = c("V1", 
"V2", "V3"), class = "data.frame", row.names = c(NA, -6L))

Convert the data columns to numeric class before you try the above code

dat1[] <- lapply(dat1, function(x) as.numeric(as.character(x))) 
dat2[] <- lapply(dat2, function(x) as.numeric(as.character(x)))