[R] Problems with merge

arun smartpink111 at yahoo.com
Wed May 29 08:33:42 CEST 2013


HI,
Possibly R FAQ: 7.31

 data1New<-data1
 data1New$A<- round(data1New$A,2)
 data2New<- data2
 data2New$A<- round(data2New$A,2)

merge(data1New,data2New,by="A")
#    A   B    C
#1 0.0 0.9 10.0
#2 1.1 0.6 11.1
#3 1.4 0.7 11.4
#4 3.1 0.4 13.1 
#5 4.4 0.8 14.4
A.K.



Hello, 

Lets say we have these two data frames: 

data1<-data.frame(c(1.23,1.363332,6.43209,4.230593,3.10294,5.09333,1.1,1.4,4.4,0),seq(0,by=0.1,length.out=10)) 
names(data1)<-c("A","B") 

data2<-data.frame(seq(0,6,by=0.1),seq(10,16,by=0.1)) 
names(data2)<-c("A","C") 

And we would like to merge only the similar values from column "A". 

merge(data1,data2,by="A",all=FALSE) 

we get: 

    A   B    C 
1 0.0 0.9 10.0 
2 1.1 0.6 11.1 
3 4.4 0.8 14.4 

Unfortunately, it's missing the value of 1.4 in both data.frame columns "A". 

Similarly, if we instead use: 

merge(data1,data2,by="A",all=TRUE) 

the value of 1.4 is duplicated while 0, 1.1, and 4.4 is not. 
All of the mathematical functions work as they should on the 1.4, 
yet merge seems to think that the two 1.4 in the different data frames 
are completely different values. 
I must be going crazy, because I use the merge function all the time and I've never run into this problem before. 

Thanks.   




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