Ariel - 6 months ago 27

R Question

This is my dataframe:

`df <- data.frame(ID = c(1,2,3), A1 = c("a1","a3","a5"),`

B1 = c("b1","b3","b5"), A2 = c("a2","a4","a6"), B2 = c("b2","b4","b6"))

And the result I want is this:

`ID A B`

1 1 a1 b1

2 1 a2 b2

3 2 a3 b3

4 2 a4 b4

5 3 a5 b5

6 3 a6 b6

I tried to approach to a solution, but I had no luck.

Answer

We can use `melt`

from `data.table`

which can take multiple `measure`

`patterns`

to convert from 'wide' to 'long' format.

```
library(data.table)
melt(setDT(df), measure = patterns("^A", "^B"),
value.name = c("A", "B"))[, variable := NULL][order(ID)]
# ID A B
#1: 1 a1 b1
#2: 1 a2 b2
#3: 2 a3 b3
#4: 2 a4 b4
#5: 3 a5 b5
#6: 3 a6 b6
```