I have some code like the following,

install.packages('farff')
library(data.table)
library(parallel)
library(cluster)
library(clusterCrit)
library(TSrepr)
library(OpenML)
library(ggplot2)
library(grid)
library(animation)
library(gganimate)
library(av)
help(melt.data.table)
data <- OpenML::getOMLDataSet(data.id = 41060)
data <- data.matrix(data$data)
data_cons <- data[1:1000,]
period <- 48
data_ave_prof <- repr_matrix(data_cons,
                             func = repr_seas_profile,
                             args = list(freq = period,
                                         func = median),
                             normalise = TRUE,
                             func_norm = norm_z)
res_clust <- kmeans(data_ave_prof, 12, nstart = 20)
data_plot <- data.table(melt(data_ave_prof))

After running the code I get the following error for the last line:

Error in value[[3L]](cond) : 
  The melt generic in data.table has been passed a matrix, but data.table::melt currently only has a method for data.tables. Please confirm your input is a data.table, with setDT(data_ave_prof) or as.data.table(data_ave_prof). If you intend to use a method from reshape2, try installing that package first, but do note that reshape2 is deprecated and you should be migrating your code away from using it.

I wrote data_plot <- as.data.table(melt(data_ave_prof)) also as its suggestion I wrote setDT(data_ave_prof) but I still get the error. I appreciate if anyone can help me how can I solve it because as I know the reshape2 package is also deprecated.

CodePudding user response：

Using data.table version 1.12.8:

data.table(melt(data_ave_prof))
       Var1 Var2       value
    1:    1    1 -0.06044068
    2:    2    1  0.60850922
    3:    3    1 -0.44836580
    4:    4    1 -0.68961528
    5:    5    1 -0.42482366
   ---                      
47996:  996   48 -0.38559291
47997:  997   48 -0.82121111
47998:  998   48 -0.51615180
47999:  999   48 -0.57098370
48000: 1000   48  0.26181203
Warning message:
In melt(data_ave_prof) :
  The melt generic in data.table has been passed a matrix and will attempt to redirect to the relevant reshape2 method; please note that reshape2 is deprecated, and this redirection is now deprecated as well. To continue using melt methods from reshape2 while both libraries are attached, e.g. melt.list, you can prepend the namespace like reshape2::melt(data_ave_prof). In the next version, this warning will become an error.

Note the end of the warning, which says the next version will turn this into an error (as you encountered).

Converting it to a data.table, you can do:

data_plot <- melt(as.data.table(data_ave_prof))
data_plot 
       variable       value
    1:       V1 -0.06044068
    2:       V1  0.60850922
    3:       V1 -0.44836580
    4:       V1 -0.68961528
    5:       V1 -0.42482366
   ---                     
47996:      V48 -0.38559291
47997:      V48 -0.82121111
47998:      V48 -0.51615180
47999:      V48 -0.57098370
48000:      V48  0.26181203
Warning message:
In melt.data.table(as.data.table(data_ave_prof)) :
  id.vars and measure.vars are internally guessed when both are 'NULL'. All non-numeric/integer/logical type columns are considered id.vars, which in this case are columns []. Consider providing at least one of 'id' or 'measure' vars in future.

It gives a new warning because it's having to guess id.vars and measure.vars because no arguments were provided except data.

data_plot <- melt(data = as.data.table(data_ave_prof), 
                  measure.vars = paste0("V", 1:48))
data_plot
       variable       value
    1:       V1 -0.06044068
    2:       V1  0.60850922
    3:       V1 -0.44836580
    4:       V1 -0.68961528
    5:       V1 -0.42482366
   ---                     
47996:      V48 -0.38559291
47997:      V48 -0.82121111
47998:      V48 -0.51615180
47999:      V48 -0.57098370
48000:      V48  0.26181203

Explicitly setting the measure.vars results in no warning. This is just one way to do that.