[R] Merge two dataframe with "by", and problems with the common field

[Jeff Newmiller]

Either d1$a and d2$a are always the same, or they are not.

If they are already the same, you can either omit one of them in the merge:

merge(d1, d2[,-2], by="b")

or you can use a set of columns for your by:

merge(d1,d2, by=c("a","b"))

If the "a" columns are distinct, then at least one of them needs a new name in the merged table, and the simplest option is to rename the columns appropriately in d1 and d2 (since they apparently represent different data anyway).
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jpm miao <miaojpm at gmail.com> wrote:

>Hi,
>
> From time to time I merge two dataframes with possibly a common field.
>Then the common field is no longer present,but what are present
>fieldname.x
>and fieldname.y. How can I fix the problem so that I can still call by
>the
>orignal fieldname? If you don't understand my problem, please see the
>example below.
>
>   Thanks
>
>Miao
>
>
>> d1
>  a b c
>1 1 4 5
>2 2 5 6
>3 3 6 7
>> d2
>  d a  f b
>1 6 1  8 4
>2 7 2  9 5
>3 8 3 10 6
>> d3<-merge(d1, d2, by="b")
>> d3
>  b a.x c d a.y  f
>1 4   1 5 6   1  8
>2 5   2 6 7   2  9
>3 6   3 7 8   3 10
>> d3["a"]
>Error in `[.data.frame`(d3, "a") : undefined columns selected
>> d3["a.x"]
>  a.x
>1   1
>2   2
>3   3
>
>	[[alternative HTML version deleted]]
>
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