[Support] Efficient reshaping with melt - Error: measure variables not found in data

[BarkleyBG]

I want to "efficiently reshape" my data using the new list functionality. But I can't even get a simple example to work with the list notation.

I'm starting with a clean environment in an RMarkdown script in a package I'm working on. Note that I'm running R 3.2.3.

library(data.table)
# data.table 1.10.4
 # The fastest way to learn (by data.table authors): https://www.datacamp.com/courses/data-analysis-the-data-table-way
 # Documentation: ?data.table, example(data.table) and browseVignettes("data.table")
 # Release notes, videos and slides: http://r-datatable.com
#Warning message:
#package ‘data.table’ was built under R version 3.2.5 

toy dataset, and it works fine in the usual case

toy <- data.frame(aa = 3:4, ab= 5:6)
t1 <- melt(data = toy, measure.vars=1:2)
t1
#  variable value
#1       aa     3
#2       aa     4
#3       ab     5
#4       ab     6

But this fails with the list notation

 t2 <- melt(data = toy,measure.vars = list(1:2))
#Error: measure variables not found in data: 1:2
 t2
#Error: object 't2' not found

I'm also having troubles with the patterns. Should I load reshape2 first? I tried that and it didn't seem to work.

 t3 <- melt(data = toy,measure.vars = patterns("^a_"))
#Error in melt_check(data, id.vars, measure.vars, variable.name, value.name) : 
  #could not find function "patterns"
 t3
#Error: object 't3' not found

fwiw

> sessionInfo()
R version 3.2.3 (2015-12-10)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.10.4

loaded via a namespace (and not attached):
[1] magrittr_1.5   plyr_1.8.4     tools_3.2.3    reshape2_1.4.1 Rcpp_0.12.4    stringi_1.1.2 
[7] stringr_1.2.0 

Thanks for your help!

[MichaelChirico]

you've tried to call a data.table method on a data.frame. please try stackoverflow if you'd like programming help

…

On Jul 13, 2017 8:45 PM, "Brian G. Barkley" ***@***.***> wrote: I want to "efficiently reshape" my data using the new list functionality. But I can't even get a simple example to work with the list notation. I'm starting with a clean environment in an RMarkdown script in a package I'm working on. Note that I'm running R 3.2.3. library(data.table) # data.table 1.10.4 # The fastest way to learn (by data.table authors): https://www.datacamp.com/courses/data-analysis-the-data-table-way # Documentation: ?data.table, example(data.table) and browseVignettes("data.table") # Release notes, videos and slides: http://r-datatable.com #Warning message: #package ‘data.table’ was built under R version 3.2.5 toy dataset, and it works fine in the usual case toy <- data.frame(aa = 3:4, ab= 5:6) t1 <- melt(data = toy, measure.vars=1:2) t1 # variable value #1 aa 3 #2 aa 4 #3 ab 5 #4 ab 6 But this fails with the list notation t2 <- melt(data = toy,measure.vars = list(1:2)) #Error: measure variables not found in data: 1:2 t2 #Error: object 't2' not found t3 <- melt(data = toy,measure.vars = patterns("^a_")) #Error in melt_check(data, id.vars, measure.vars, variable.name, value.name) : could not find function "patterns" t3 #Error: object 't3' not found fwiw > sessionInfo() R version 3.2.3 (2015-12-10) Platform: x86_64-w64-mingw32/x64 (64-bit) Running under: Windows 7 x64 (build 7601) Service Pack 1 locale: [1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252 [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C [5] LC_TIME=English_United States.1252 attached base packages: [1] stats graphics grDevices utils datasets methods base other attached packages: [1] data.table_1.10.4 loaded via a namespace (and not attached): [1] magrittr_1.5 plyr_1.8.4 tools_3.2.3 reshape2_1.4.1 Rcpp_0.12.4 stringi_1.1.2 [7] stringr_1.2.0 Thanks for your help! — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2270>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AHQQdfEoIGs3K_CMUeHmVSX-4qQ9S7boks5sNuRGgaJpZM4OXy6A> .

[BarkleyBG]

And indeed, what a silly mistake it is

toy <- data.frame(aa = 3:4, ab= 5:6) %>% 
    as.data.table() ### fixes everything, obviously

t2 <- melt(data = toy,measure.vars = list(1:2)) ###now works
t2  
#   variable value
#1:       aa     3
#2:       aa     4
#3:       ab     5
#4:       ab     6

[MichaelChirico]

you can just declare it with data.table to start, or use setDT if the object exists

…

On Jul 13, 2017 9:07 PM, "Brian G. Barkley" ***@***.***> wrote: Closed #2270 <#2270>. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#2270 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AHQQdUhfaNnT0zP3AXQWVYlR9O8Z0x1Dks5sNumHgaJpZM4OXy6A> .