Thank you dear friends.  You have cleared my first doubt.  

My second doubt:
I have the same data sets "Elder" and "Younger". Elder <- data.frame(
  ID=c("ID1","ID2","ID3"),
  age=c(38,35,31))
Younger <- data.frame(
  ID=c("ID4","ID5","ID3"),
  age=c(29,21,"NA"))


 Row ID3 comes in both data set. It has a value (31) in "Elder" while "NA" in "Younger".

I need output like this.

ID    age
ID1  38
ID2  35
ID3  31
ID4  29
ID5  21 

Kindly help me.



On Thursday, 16 January 2014 9:16 PM, Marc Schwartz-3 [via R] <ml-node+s789695n4683682h69@n4.nabble.com> wrote:
 
Not quite: 

> rbind(Elder, Younger) 
   ID age 
1 ID1  38 
2 ID2  35 
3 ID3  31 
4 ID4  29 
5 ID5  21 
6 ID3  31 

Note that ID3 is duplicated. 


Should be: 

> merge(Elder, Younger, by = c("ID", "age"), all = TRUE) 
   ID age 
1 ID1  38 
2 ID2  35 
3 ID3  31 
4 ID4  29 
5 ID5  21 


He wants to do a join on both "ID" and "age" to avoid duplications of rows when the same ID and age occur in both data frames. If the same column names (eg "Var") appears in both data frames and are not part of the 'by' argument, you end up with Var.x and Var.y in the result. 

In the case of two occurrences of the same ID but two different ages, if that is possible, both rows would be added to the result using the above code. 

Regards, 

Marc Schwartz 


On Jan 16, 2014, at 9:04 AM, Frede Aakmann Tøgersen <[hidden email]> wrote: 

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