R help - Sep 2010 - How to compare, match two columns from diferent dataframe and assign values from one datafram to the other

Dear R experts,

I'm new to R. It seems to be a simple question but I just can't find a
way to do it. Please help me.

I have two data sets x and y as shown in the following. I want to compare the
first two columns in x and y, find the matched ones and assign the relative
value from column 2 of y to generate the third column of x. Any help wil be
appreciated. Thanks.
> x
      [,1] [,2]
 [1,] "1"  "0"
 [2,] "2"  "0"
 [3,] "3"  "0"
 [4,] "4"  "0"
 [5,] "5"  "0"
 [6,] "6"  "0"
 [7,] "7"  "0"
 [8,] "8"  "0"
 [9,] "9"  "0"
[10,] "10" "0"
> y
     [,1] [,2]
[1,] "7"  "a"
[2,] "4"  "b"
[3,] "2"  "c"
[4,] "8"  "d"
[5,] "12" "e"
[6,] "15" "f"

The result I expect is:
x
      [,1] [,2] [,3]
 [1,] "1"  "0"  NA
 [2,] "2"  "0"  "c"
 [3,] "3"  "0"  NA
 [4,] "4"  "0"  "b"
 [5,] "5"  "0"  NA
 [6,] "6"  "0"  NA
 [7,] "7"  "0"  "a"
 [8,] "8"  "0"  "d"
 [9,] "9"  "0"  NA
[10,] "10" "0" NA


Best,

Ying

Hi:

df <- data.frame(x = 1:10, y = rep(0, 10))
dg <- data.frame(x = c(7, 4, 2, 8, 12, 15), y = letters[1:6])
merge(df, dg, by = 'x', all.x = TRUE)
    x y.x  y.y
1   1   0 <NA>
2   2   0    c
3   3   0 <NA>
4   4   0    b
5   5   0 <NA>
6   6   0 <NA>
7   7   0    a
8   8   0    d
9   9   0 <NA>
10 10   0 <NA>

HTH,
Dennis

On Fri, Sep 17, 2010 at 2:02 PM, Wang, Ying <Ying.Wang@uth.tmc.edu> wrote:
> Dear R experts,
>
> I'm new to R. It seems to be a simple question but I just can't
find a way
> to do it. Please help me.
>
> I have two data sets x and y as shown in the following. I want to compare
> the first two columns in x and y, find the matched ones and assign the
> relative value from column 2 of y to generate the third column of x. Any
> help wil be appreciated. Thanks.
>
> > x
>      [,1] [,2]
>  [1,] "1"  "0"
>  [2,] "2"  "0"
>  [3,] "3"  "0"
>  [4,] "4"  "0"
>  [5,] "5"  "0"
>  [6,] "6"  "0"
>  [7,] "7"  "0"
>  [8,] "8"  "0"
>  [9,] "9"  "0"
> [10,] "10" "0"
> > y
>     [,1] [,2]
> [1,] "7"  "a"
> [2,] "4"  "b"
> [3,] "2"  "c"
> [4,] "8"  "d"
> [5,] "12" "e"
> [6,] "15" "f"
>
> The result I expect is:
> x
>      [,1] [,2] [,3]
>  [1,] "1"  "0"  NA
>  [2,] "2"  "0"  "c"
>  [3,] "3"  "0"  NA
>  [4,] "4"  "0"  "b"
>  [5,] "5"  "0"  NA
>  [6,] "6"  "0"  NA
>  [7,] "7"  "0"  "a"
>  [8,] "8"  "0"  "d"
>  [9,] "9"  "0"  NA
> [10,] "10" "0" NA
>
>
> Best,
>
> Ying
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
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