Hello,

I am relatively new to R and I am struggling with the following problem:

I have a data frame that consists of two sets of x and y variables i.e. x1, y1 and x2, y2.

I would like to use gather or any other function that could help to create a new data frame with

merged x1 and x2 variables into a single x variable. I have tried to use gather but can see only examples applied to data frames with a single x variable.

Bellow is my reprex with the desired output as well.

Your help is really appreciated. Thank you!

```
library(tidyr)
(df <- data.frame(x1=c(1,2,3),y1=c(10,14,12), x2=c(2,3,4),y2=c(12,13,11)))
#> x1 y1 x2 y2
#> 1 1 10 2 12
#> 2 2 14 3 13
#> 3 3 12 4 11
(df_tall <- gather(df,"z", "y", y1:y2))
#> x1 z y
#> 1 1 y1 10
#> 2 2 y1 14
#> 3 3 y1 12
#> 4 1 x2 2
#> 5 2 x2 3
#> 6 3 x2 4
#> 7 1 y2 12
#> 8 2 y2 13
#> 9 3 y2 11
# desired output
print('Desired output')
#> [1] "Desired output"
(df_mod <- data.frame(x=c(1,2,2,3,3,4),y=c(10,14,12,12,13,11), z=c("y1", "y1", "y2", "y1", "y2", "y2")))
#> x y z
#> 1 1 10 y1
#> 2 2 14 y1
#> 3 2 12 y2
#> 4 3 12 y1
#> 5 3 13 y2
#> 6 4 11 y2
```

^{Created on 2020-04-03 by the reprex package (v0.2.1)}