R help - May 2010 - Match 2 vectors

Hi,

I have 2 dataframes of unequal length, and I would like to match a
factor to them so that both dataframes will have the same number of
rows.

example:
# create the 2 dataframes with unequal length
data1 <- data.frame(letters, 1:26)[-c(5,10,19:21),]
data2 <- data.frame(letters, 1:26)[-c(6,9,15:18),]


data2a <- match(data1[,1], data2[,1])
data2b <- data2[data2a,]

When I match data1 to data2, and combine the data2a vector to the
original data2, I'm still missing some rows. I need to get the 26
rows, and preferably with the first column displaying all the levels.
In data2b the mismatches show up as NA in the whole row.

Thanks.
Kang Min

Hi:

On Thu, May 27, 2010 at 10:26 PM, Kang Min <ngokangmin@gmail.com> wrote:
> Hi,
>
> I have 2 dataframes of unequal length, and I would like to match a
> factor to them so that both dataframes will have the same number of
> rows.
>
> example:
> # create the 2 dataframes with unequal length
> data1 <- data.frame(letters, 1:26)[-c(5,10,19:21),]
> data2 <- data.frame(letters, 1:26)[-c(6,9,15:18),]
>
If this is your real problem, then an easy thing to do is

    data1 <- data2 <- data.frame(letters[1:26])
    data1[c(5,10,19:21), ] <- NA
    data2[c(6, 9, 15:18), ] <- NA
    data3 <- cbind(data1, data2)
    names(data3, c('lett1', 'lett2'))
    data3

However, I suspect this is not your real problem, so let's add a variable to
each of the data frames you posted and try again:

data1 <- data.frame(letters, 1:26)[-c(5,10,19:21),]
data2 <- data.frame(letters, 1:26)[-c(6,9,15:18),]

data1$x <- rpois(nrow(data1), 10)
data2$y <- rpois(nrow(data2), 5)

# Now merge data1 and data2:
(data3 <- merge(data1, data2, all = TRUE))

   letters X1.26  x  y
1        a     1  7  1
2        b     2 13  3
3        c     3 10  5
4        d     4  4  9
5        e     5 NA  4
6        f     6 10 NA
7        g     7 15  4
8        h     8 10  6
9        i     9 12 NA
10       j    10 NA  3
11       k    11  8  6
12       l    12 12  3
13       m    13 10  3
14       n    14  7  8
15       o    15  6 NA
16       p    16  8 NA
17       q    17  6 NA
18       r    18  4 NA
19       s    19 NA  2
20       t    20 NA  6
21       u    21 NA  4
22       v    22 12  6
23       w    23 10  3
24       x    24  7  8
25       y    25  9  6
26       z    26 15  7

To get rid of the second column, set data3[, 2] <- NULL.

HTH,
Dennis

> data2a <- match(data1[,1], data2[,1])
> data2b <- data2[data2a,]
>
> When I match data1 to data2, and combine the data2a vector to the
> original data2, I'm still missing some rows. I need to get the 26
> rows, and preferably with the first column displaying all the levels.
> In data2b the mismatches show up as NA in the whole row.
>
> Thanks.
> Kang Min
>
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