feat(7614): added redirection of data.frame at dcast and melt to dcast.data.table and melt.data.table #7634

manmita · 2026-01-27T20:45:21Z

I added tests for data.frame to check if dcast and melt work directly but got the following error

Running test id 2365.1         Test 2365.1 produced 1 errors but expected 0
Expected: 
Observed: no applicable method for 'melt' applied to an object of class "data.frame"
Running test id 2365.2         Test 2365.2 produced 1 errors but expected 0
Expected: 
Observed: no applicable method for 'dcast' applied to an object of class "data.frame"

Hence redirected data.frame to dcast.data.table directly similarly for melt

github-actions · 2026-01-27T21:07:06Z

No obvious timing issues in HEAD=fix/dcast_melt_for_data.frame

Generated via commit 3cfe6a0

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	3 minutes and 3 seconds
Installing different package versions	23 seconds
Running and plotting the test cases	4 minutes and 9 seconds

MichaelChirico · 2026-01-27T21:14:28Z

R/fcast.R

+dcast.data.frame = function(data, ...) {
+  if (!is.data.frame(data)) stopf("'%s' must be a data.frame", "data")
+  data = as.data.table(data)
+  dcast.data.table(data, ...)


Just remove the error in dcast.data.table. Don't coerce.

MichaelChirico · 2026-01-27T21:19:30Z

R/fmelt.R

  ans
 }
+
+melt.data.frame = function(data, ...) {


I think this constitutes a breaking change for packages/scripts using both {data.table} and {reshape2} (e.g. {WebAnalytics} or {BTSPAS}), which might result in the wrong S3 method being invoked.

Please investigate the interaction of your update with {reshape2}, e.g. the load order.

I think the solution is not to have a data.frame method, but to fake one in the dcast() generic like:

dcast = function(x, ...) { if (!is.data.table(x) && is.data.frame(x)) return(dcast.data.table(x, ...)) UseMethod("dcast") }

have redirected data.frame to the dcast.data.table
currently fixing a few errors

Running test id 2365.2 Test 2365.2 produced 1 errors but expected 0 Expected: Observed: argument "formula" is missing, with no default Test 2365.2 produced 1 messages but expected 0 Expected: Observed: Using 'v' as value column. Use 'value.var' to override

Will update the PR once this is fixed

codecov · 2026-01-27T21:22:25Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.02%. Comparing base (b537ec4) to head (3cfe6a0).
⚠️ Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7634   +/-   ##
=======================================
  Coverage   99.02%   99.02%           
=======================================
  Files          87       87           
  Lines       16890    16896    +6     
=======================================
+ Hits        16726    16732    +6     
  Misses        164      164

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…e for dcast/melt

manmita · 2026-01-27T22:34:57Z

Hii @MichaelChirico without coercing it is failing the following test

df_dcast = data.frame(a = c("x", "y"), b = 1:2, v = 3:4)
dt_dcast = data.table(a = c("x", "y"), b = 1:2, v = 3:4)
test(2365.2, dcast(df_dcast, a ~ b, value.var = "v"), dcast(dt_dcast, a ~ b, value.var = "v"))

error: object of type 'symbol' is not subsettable

Will need to test out the point of crash (using gdb) - will check it out tomorrow ^^

… and melt.data.table

manmita · 2026-01-28T22:23:22Z

Found the issue

The way we discussed to use the following

dcast = function(x, ...) {
  if (!is.data.table(x) && is.data.frame(x)) return(dcast.data.table(x, ...))
  UseMethod("dcast")
}

It was failing at the following lines

 m = as.list(match.call()[-1L])
  subset = m[["subset"]][[2L]]

This is using match call hence m contains data, formula etc meaning m[["subset"]] = subset
hence this was crashing when subset was supposed to be null.

The soln is to use match call at the dcast function and find the user args and forward it and redirect it to dcast.data.table

Although this crash only occured in dcast and a return worked for melt but I have still changed both but I am not sure which will be more optimal perf wise

Let me know if anything needs to be changed or anything can be optimized in this case

Thanks

MichaelChirico · 2026-01-29T00:27:13Z

inst/tests/tests.Rraw

-test(1953.4, melt.data.table(DT, id.vars = 'id', measure.vars = 'a'),
-             error = "must be a data.table")
+expected = data.table(id = rep(DT$id, 2), variable = factor(rep(c("a1", "a2"), each = 3)), value = c(DT$a1, DT$a2))
+test(1953.4, melt.data.table(DT, id.vars = "id", measure.vars = c("a1", "a2")), expected)


If we can avoid calling private functions, that's great. Does this test still work with just using melt(DT, ...)?

This test is labeled as being for "coverage", for which purpose we sometimes break the public API, but now that it's possible to send a data.frame through to melt.data.table(), ideally we can stick to the public API even in the test.

yeah, it does, will change it to melt

MichaelChirico · 2026-01-29T00:29:36Z

inst/tests/tests.Rraw

     message = 'Using.*value column.*override')
 setDF(DT)
-test(1962.085, dcast.data.table(DT), error = 'must be a data.table')
+test(1962.085, guess(DT), 'V',


this changes the nature of the test a fair amount. Why just just test agains the output dcast(DT) for some trivial formula?

Or perhaps, we can just drop this test and mark it with a comment "removed test of error case for dcast() passed a data.frame for #7614"

MichaelChirico · 2026-01-29T00:29:47Z

inst/tests/tests.Rraw

+# test for data.frame reshape for dcast
+df_dcast = data.frame(a = c("x", "y"), b = 1:2, v = 3:4)
+dt_dcast = data.table(a = c("x", "y"), b = 1:2, v = 3:4)
+test(2365.2, dcast(df_dcast, a ~ b, value.var = "v"), dcast(dt_dcast, a ~ b, value.var = "v"))


restore trailing newline

MichaelChirico · 2026-01-29T00:34:00Z

R/fcast.R

+    eval(mc, parent.frame())
+  }
+  else {
+    UseMethod("dcast", data)
+  }


Suggested change

eval(mc, parent.frame())

}

else {

UseMethod("dcast", data)

}

return(eval(mc, parent.frame()))

}

UseMethod("dcast", data)

MichaelChirico · 2026-01-29T00:36:24Z

R/fmelt.R

+    eval(mc, parent.frame())
+  }
+  else {
+    UseMethod("melt", data)
+  }


Suggested change

eval(mc, parent.frame())

}

else {

UseMethod("melt", data)

}

return(eval(mc, parent.frame()))

}

UseMethod("melt", data)

MichaelChirico · 2026-01-29T00:38:47Z

R/fcast.R

-  UseMethod("dcast", data)
+  if (!is.data.table(data) && is.data.frame(data)){
+    mc <- match.call()
+    mc[[1L]] <- as.name("dcast.data.table")


Can you confirm this works outside the test suite?

R CMD INSTALL data.table Rscript -e "library(data.table); dcast(mtcars, cyl ~ gear, value.var='wt', fun.aggregate=mean)"

I am not sure without running it myself whether the frame in which mc is evaluated will be able to see dcast.data.table given that it's not exported.

In the test suite, we define dcast.data.table = data.table:::dcast.data.table, so the test passing is not enough to resolve my apprehension.

> dcast(mtcars, cyl ~ gear, value.var='wt', fun.aggregate=mean) Key: <cyl> cyl 3 4 5 <num> <num> <num> <num> 1: 4 2.465000 2.378125 1.8265 2: 6 3.337500 3.093750 2.7700 3: 8 4.104083 NaN 3.3700

This is the output for dcast of mtcars
gives the same output on converting it to data.table

> a = as.data.table(mtcars) > dcast(a, cyl ~ gear, value.var='wt', fun.aggregate=mean) Key: <cyl> cyl 3 4 5 <num> <num> <num> <num> 1: 4 2.465000 2.378125 1.8265 2: 6 3.337500 3.093750 2.7700 3: 8 4.104083 NaN 3.3700

I had also printed the m values while debugging (line 170 of fcast)
and the results for data.table and data.frame were same after these changes and were as expected
eg: m["data"] was giving dt_dcast which was the user arg passed.

> dcast(mtcars, cyl ~ gear, value.var='wt', fun.aggregate=mean) $data mtcars $formula cyl ~ gear $fun.aggregate mean $value.var [1] "wt" Key: <cyl> cyl 3 4 5 <num> <num> <num> <num> 1: 4 2.465000 2.378125 1.8265 2: 6 3.337500 3.093750 2.7700 3: 8 4.104083 NaN 3.3700 >

when printing m values

manmita · 2026-01-29T03:41:38Z

Updated with the suggested changes ^^

manmita added 2 commits January 28, 2026 02:10

feat(7614): added s3 method at dcast and melt for data.frame

b0a9b0f

feat(7614): added to news

00fa021

manmita requested review from MichaelChirico and tdhock as code owners January 27, 2026 20:45

manmita added 2 commits January 28, 2026 02:16

feat(7614): code styling

c50d1dc

feat(7614): bug fix on dcast

fa909a6

manmita marked this pull request as draft January 27, 2026 20:59

feat(7614): added s3method to namespace

9cc619b

MichaelChirico reviewed Jan 27, 2026

View reviewed changes

feat(7614): fix test 2365.1 as its calling undefined columns

6502e86

manmita marked this pull request as ready for review January 27, 2026 21:17

MichaelChirico reviewed Jan 27, 2026

View reviewed changes

manmita added 2 commits January 28, 2026 03:53

feat(7614): removed s3method and used redirection incase of data.fram…

b4cd9ed

…e for dcast/melt

feat(7614): code linting

a05b069

manmita changed the title ~~feat(7614): added s3 method at dcast and melt for data.frame~~ feat(7614): added redirection of data.frame at dcast and melt to dcast.data.table and melt.data.table Jan 27, 2026

feat(7614): use call to capture args and redirect to dcast.data.table…

a3e5465

… and melt.data.table

manmita requested a review from MichaelChirico January 28, 2026 22:26

MichaelChirico reviewed Jan 29, 2026

View reviewed changes

feat(7614): updated tests and dcast, melt

3cfe6a0

manmita requested a review from MichaelChirico January 29, 2026 03:41

feat(7614): added redirection of data.frame at dcast and melt to dcast.data.table and melt.data.table #7634

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feat(7614): added redirection of data.frame at dcast and melt to dcast.data.table and melt.data.table #7634

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