Binding

“In God we trust, all others bring data.” — W Edwards Deming

When thinking about combining two data frames one has to distinguish between merging them by the values given in a specific column or consecutively putting them together just rows after rows.

For the following examples, we will use these two data frames.

x <- c(1, 2, 3, 4, 5)
y <- c(1.4, 2.5, 3.6, 4.0, 5.5)
z <- c("A", "B", "C", "D", "E")

df1 <- data.frame(X = x, Y = y, Z = z)
df1

##   X   Y Z
## 1 1 1.4 A
## 2 2 2.5 B
## 3 3 3.6 C
## 4 4 4.0 D
## 5 5 5.5 E

y <- c(14, 25, 36, 40, 55)
x <- c(100, 200, 300, 400, 500)
z <- c("A", "C", "E", "D", "B")
df2 <- data.frame(X = x, Y = y, Z = z)
df2

##     X  Y Z
## 1 100 14 A
## 2 200 25 C
## 3 300 36 E
## 4 400 40 D
## 5 500 55 B

To combine two data frames, use the rbind function provided that both data frames have the same column names and the same number of columns.

dfr <- rbind(df1, df2)
dfr

##      X    Y Z
## 1    1  1.4 A
## 2    2  2.5 B
## 3    3  3.6 C
## 4    4  4.0 D
## 5    5  5.5 E
## 6  100 14.0 A
## 7  200 25.0 C
## 8  300 36.0 E
## 9  400 40.0 D
## 10 500 55.0 B

Note, that it is not necessary that the columns are in the same order since the concatenation is done by the column names, not the column sequence:

df3 <- df2[,c(1,3,2)]
df3

##     X Z  Y
## 1 100 A 14
## 2 200 C 25
## 3 300 E 36
## 4 400 D 40
## 5 500 B 55

dfr <- rbind(df1, df3)
dfr

##      X    Y Z
## 1    1  1.4 A
## 2    2  2.5 B
## 3    3  3.6 C
## 4    4  4.0 D
## 5    5  5.5 E
## 6  100 14.0 A
## 7  200 25.0 C
## 8  300 36.0 E
## 9  400 40.0 D
## 10 500 55.0 B