comparing the value of the first column of two dataframe to find the index of the same values in R?

Question

what I wanted to do is to compare the first column of two data frame and find the indexes of the same value and assign the element of the second column of the first dataframe to the second dataframe : please see the example :

datafranmeA          dataframeB

   id   number         id   
1  1     45             1
2  3     78             4
3  5     67             12
4  12    18             5
5  4     44             8
6  8      32
7  13     41

output : dataframeB

         id     number
     1    1      45
     2    4      44
     3    12     18
     4    5      67
     5    8      32

I use a two for loop and if to compare but it is really slow as my own data is really big , how should I speed it up ?

for (i in 1:length(A[,1])){
 for (j in 1:length(B[,1])){
   if (A[i,1]==B[j,1]) {
      B[j,2]=A[i,2]}}}

thank you in advance,

score 0 · Accepted Answer · answered Nov 29 '14 at 13:42

0

Try

library(dplyr)
left_join(dataframeB, dataframeA)

answered Nov 29 '14 at 13:42

KFB

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,thanks, that was so helpful, waiting for other answer but yours is perfect – user3813088 Nov 29 '14 at 13:50
,what if it has other column as well ? – user3813088 Nov 29 '14 at 13:57
Suggest to provide sample data so that we could understand the problem better. Also, it's good to have a look at the link suggested by @beginneR – KFB Nov 29 '14 at 14:03
thanks , i mean that the dataframe have other column but not usable here – user3813088 Nov 29 '14 at 14:14

comparing the value of the first column of two dataframe to find the index of the same values in R?

1 Answers1