Pivot_longer on all columns

Question

I am using pivot_longer from tidyr to transform a data frame from wide to long. I wish to use all the columns and maintain rownames in a column as well. The earlier melt function works perfect on this call

w1 <- reshape2::melt(w)
head(w1)
'data.frame':   900 obs. of  3 variables:
 $ Var1 : Factor w/ 30 levels "muscle system process",..: 1 2 3 4 5 6 7 8 9 10 ...
 $ Var2 : Factor w/ 30 levels "muscle system process",..: 1 1 1 1 1 1 1 1 1 1 ...
 $ value: num  NA NA NA NA NA NA NA NA NA NA ...

But pivot_longer doesnt

w %>% pivot_longer()

Error in UseMethod("pivot_longer") : 
  no applicable method for 'pivot_longer' applied to an object of class "c('matrix', 'array', 'double', 'numeric')"

Any suggestion is appreciated

Answer 1

Obviously some data would be helpful, but your problem lies in the fact that you are using pivot_longer() on an object of class matrix and not data.frame

library(tidyr)

# your error
mycars <- as.matrix(mtcars)
pivot_longer(mycars)

Error in UseMethod("pivot_longer") : 
  no applicable method for 'pivot_longer' applied to an object of class
  "c('matrix', 'array', 'double', 'numeric')"

pivot_longer() will work on a data frame

> class(mycars)
[1] "matrix" "array" 
> class(mtcars)
[1] "data.frame"

Remember to specify the cols argument, this was not required in reshape2::melt() (more info in the documentation). You want all the columns so cols = everything():

pivot_longer(mtcars, cols = everything())

(Disclaimer: Of course, mtcars is not the best dataset to convert to long format)