Add one column below another in a data.frame in R

Question

Not sure if I used the correct english words in the subject to describe what I need.

See this example

df <- data.frame(a=sample(1:10), b=sample(1:10))
df
    a  b
1   2  9
2   5  8
3  10  1
4   3  7
5   8  4
6   6 10
7   9  5
8   7  6
9   1  3
10  4  2

I want to take b column at put it below a as 10 new rows.

    a
1   2
2   5
3  10
4   3
5   8
6   6
7   9
8   7
9   1
10  4
11  9
12  8
13  1
14  7
15  4
16 10
17  5
18  6
19  3
20  2

I found examples with rbind but couldn't find out how to use it in my situation.

Answer 1

We can use unlist to create a vector and then wrap it with data.frame to create a new dataset.

d1 <- data.frame(a=unlist(df, use.names = FALSE))
d1
#    a
#1   2
#2   5
#3  10
#4   3
#5   8
#6   6
#7   9
#8   7
#9   1
#10  4
#11  9
#12  8
#13  1
#14  7
#15  4
#16 10
#17  5
#18  6
#19  3
#20  2

Answer 2

你也可以这样做：

df2 <- data.frame(a = c(df[,"a"], df[,"b"]))

Answer 3

You can use pivot_longer() from tidyr package.

library(dplyr)
set.seed(1)
df <- data.frame(a=sample(1:10), b=sample(1:10))
pivot_longer(df, a:b)


# A tibble: 20 x 2
   name  value
   <chr> <int>
 1 a         3
 2 b         3
 3 a         4
 4 b         2
 5 a         5
 6 b         6
 7 a         7
 8 b        10
 9 a         2
10 b         5
11 a         8
12 b         7
13 a         9
14 b         8
15 a         6
16 b         4
17 a        10
18 b         1
19 a         1
20 b         9

Answer 4

You can select a and bind it to b in the following way:

df <- data.frame(a=sample(1:10), b=sample(1:10))
df %>% 
  select(a) %>% 
  bind_rows(
    df %>% 
      transmute(a = b)
  )

Answer 5

you can just combine the variables into one

df <- data.frame(a=sample(1:10), b=sample(1:10))
df2 <- data.frame(a = c(df$a, df$b))

Answer 6

You can also use both tidyr and dplyr to end with a new data.frame.

library(tidyr)
library(dplyr)
set.seed(1)
df <- data.frame(a=sample(1:10), b=sample(11:20), c=sample(21:30))
head(df)

df2 <- pivot_longer(df, a:c, names_to = "letter", values_to = "d")
df3 <- data.frame(arrange(df2, letter))
head(df3); str(df3)

Now all three columns are combined into a 2 column data frame with 30 rows.

Be cautious with creating columns that are longer than the original data.frame, as they will repeat other columns to make the entire data.frame have the correct number of rows. This might be advantageous when repeating the subjects over and over, but could be problematic in others circumstances.

df4 <- pivot_longer(df, c(a,c), names_to = "letter", values_to = "d")
df5 <- data.frame(arrange(df4, letter))
head(df5); str(df5)
df5

Notice R duplicated column 'b' in order to make it as long as the other columns (20 char)