Merging

To merge two data frames, you have to specify the column containing the values which should be used in the matching. In this example, we use the values of the column Z to merge the two data frames.

dfc <- merge(df1, df2, by = "Z")
dfc

##   Z X.x Y.x X.y Y.y
## 1 A   1 1.4 100  14
## 2 B   2 2.5 500  55
## 3 C   3 3.6 200  25
## 4 D   4 4.0 400  40
## 5 E   5 5.5 300  36

Since both data frames have identical column names, X and Y is added to the column names in the resulting data frame to indicate if the column is from the first (i.e. X) or second (i.e. Y) data frame. You can easily rename the columns using the colnames function.

If the columns which should be used for mergin have different names, no problem: just supply the column names separately for the first (i.e. X) and second (i.e. Y) data frame:

colnames(df2) <- c("H", "I", "J")
dfc <- merge(df1, df2, by.x = "Z", by.y = "J")
dfc

##   Z X   Y   H  I
## 1 A 1 1.4 100 14
## 2 B 2 2.5 500 55
## 3 C 3 3.6 200 25
## 4 D 4 4.0 400 40
## 5 E 5 5.5 300 36

Since not only the names of the columns used for merging but all column names are different, no X or Y is added in the output column names.