Nancy - 4 months ago 23

R Question

I would like to undo a

`reshape`

`gather`

`tidyr`

`toy = data.frame(`

first_key = rep(c("A", "B", "C"), each = 6),

second_key = rep(rep(c(1:2), each = 3), 3),

colors = c("red", "yellow", "green", "blue", "purple", "beige"),

days = c("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"),

index = c(1:3)

)

Which gives the following data.frame:

`first_key second_key colors days index`

A 1 red Monday 1

A 1 yellow Tuesday 2

A 1 green Wednesday 3

A 2 blue Thursday 1

A 2 purple Friday 2

A 2 beige Saturday 3

B 1 red Monday 1

B 1 yellow Tuesday 2

B 1 green Wednesday 3

B 2 blue Thursday 1

B 2 purple Friday 2

B 2 beige Saturday 3

C 1 red Monday 1

C 1 yellow Tuesday 2

C 1 green Wednesday 3

C 2 blue Thursday 1

C 2 purple Friday 2

C 2 beige Saturday 3

Reshaping it to a wide format with numbered versions of the variables looks like this:

`toy_wide = reshape(toy, idvar = c("first_key", "second_key"),`

timevar = "index", direction = "wide", sep = "_")

And gives this wide format:

`first_key second_key colors_1 days_1 colors_2 days_2 colors_3 days_3`

A 1 red Monday yellow Tuesday green Wednesday

A 2 blue Thursday purple Friday beige Saturday

B 1 red Monday yellow Tuesday green Wednesday

B 2 blue Thursday purple Friday beige Saturday

C 1 red Monday yellow Tuesday green Wednesday

C 2 blue Thursday purple Friday beige Saturday

But how do I get it back to the original format? I've tried the following but I get an error.

`tidyr::gather(toy_wide, key = c("first_key", "second_key"), value = c("days", "colors"),`

colors_1:days_3, factor_key = TRUE)

Error: Invalid column specification

Answer

Here is another option with `melt`

from `data.table`

which can take multiple `measure`

`patterns`

.

```
library(data.table)
melt(setDT(toy_wide), measure = patterns("^colors", "^days"),
value.name = c("colors", "days"), variable.name = "index")[order(first_key, second_key)]
```