Why do I get this error message "could not find function "patterns" when using the "melt" function in data.table in R

Question

I am using the data.table (version 1.10.4) to clean data (btw, I have installed "reshape2"), but I got this message:

Error in melt_check(data, id.vars, measure.vars, variable.name, value.name) : could not find function "patterns"

I checked many times, but don't figure out why. I am posting my code below, can anyone have a look at it, and tell me where I was wrong? Thanks.

library(reshape2)
library(data.table)
library(readxl)
data<-read_excel("Time3Ratee.xlsx")
meltdata<-melt(data,id = 1:4, measure = patterns ("^ratee\\d+$","^RICB.peer\\d+\\.1", "^RICB.peer\\d+\\.2","^RICB.peer\\d+\\.3", "^TICB.peer\\d+\\.1", "^TICB.peer\\d+\\.2","^TICB.peer\\d+\\.3","^LE.peer\\d+\\.1", "^LE.peer\\d+\\.2","^LE.peer\\d+\\.3","^LE.peer\\d+\\.4", "^DEV.peer\\d+\\.1", "^DEV.peer\\d+\\.2","^DEV.peer\\d+\\.3"), value.name = c("ratee", "RICB.peer.1", "RICB.peer.2","RICB.peer.3", "TICB.peer.1", "TICB.peer.2","TICB.peer.3", "LE.peer.1", "LE.peer.2","LE.peer.3","LE.peer.4", "DEV.peer.1", "DEV.peer.2","DEV.peer.3"))

patterns is a function only supported inside data.table::melt, not reshape2::melt. You'll get the former if you are applying melt to a data.table; but with a data.frame, a matrix or whatever read_excel returns, you'll get the latter. — Frank
– Frank, Commented Feb 9, 2017 at 16:47
@Frank, Could you explain a little bit more about the data.table is the sentence of "You'll get the former if you are applying melt to a data.table"? Do you mean that I should use 'read.table' command to read the data file? — wh41e
– wh41e, Commented Feb 9, 2017 at 17:17
No, go ahead and use read_excel, but then (assuming it gives you a data.frame), use setDT before applying melt. Like data <- setDT(read_excel(...)). Your example is not reproducible, so there is no way for me to test if this works, of course. — Frank
– Frank, Commented Feb 9, 2017 at 17:19
@Frank, it works!!!!Thanks a ton. I'll go to check setDT command later. — wh41e
– wh41e, Commented Feb 9, 2017 at 17:27

David Arenburg · Accepted Answer · 2019-12-01 08:58:25Z

3

(Converting @Franks comment to an answer)

In order to be able to use data.table::melt, you need to convert your data set into a data.table class by either using using as.data.table() or setDT()

setDT(data)

Otherwise, melt will default to reshape2::melt and you won't be able to use data.tables functionality such as patterns.

edited Dec 1, 2019 at 8:58

David Arenburg

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answered Dec 1, 2019 at 3:35

zhang jing

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