Help me understand the semantics of spread()

[John Rauser]

In this code:

library(tidyr)

dat<-data.frame(var=letters[1:13],value=runif(13))

dat

spread(dat, var, value)

dat$dummy=1

spread(dat, var, value)

Why should the first spread() give me a 13 row data frame (with the values on the trace), while the second gives me a single row (which is what I wanted in the first place)?

Of course, with reshape2 I'd have to specify the dummy explicitly:

library(reshape2)

dat<-data.frame(var=letters[1:13],value=runif(13))

dat

dcast(dat, 1~var, value.var = "value")

... or use the special '.' syntax

dcast(dat, .~var, value.var = "value")

... but even the "..." syntax does what I wanted, and is closest to my first spread() above.

dcast(dat, ...~var, value.var = "value")

I guess my question is why the 13 row data frame makes sense.  Or perhaps it doesn't and I should file an issue?

Best,

-J

[Hadley Wickham]

Are you sure you have the latest tidyr? That was a bug I fixed pretty
recently I think.
Hadley

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[John Rauser]

Aha!  Updating tidyr did the trick.  I should have tried that first... I assumed that there was some good reason for that behavior that I was just missing.

Thanks!

-J