problem with cache function

[Thomas Keller]

# cache as defined gives an error (using the tutorial 'letters'
project)
> cache
function (variable)
{
save(list = variable, envir = .GlobalEnv, file =
file.path("cache",
paste(variable, ".RData", sep = "")))
}
<environment: namespace:ProjectTemplate>
> save(list = first.letter.counts, envir = .GlobalEnv, file = file.path("cache", paste('first.letter.count', ".RData", sep="")))
Error in FUN(X[[1L]], ...) : invalid first argument

However this works:
> save(first.letter.counts, envir = .GlobalEnv, file = file.path("cache", paste('first.letter.count', ".RData", sep="")))

and this works:
> save(list = c('second.letter.counts'), envir = .GlobalEnv, file = file.path("cache", paste('second.letter.count', ".RData", sep="")))

I'm new to this, so if there is a better way to approach this, please
let me know.
cheers,
Tom K

[John Myles White]

Hi Thomas,

I'll have to look into this later tonight, but my guess is that I used a calling convention for cache() in the tutorial that isn't implemented. Specifically, your example suggests that I suggested doing

cache(some.variable)

whereas you really need to run

cache('some.variable')

Does that solve your problem? If so, I'll update the docs to reflect that.

-- John

[Thomas Keller]

Hi John,

I tried cache('some.variable') too and it gave the same error. It seems that the save function takes either a scalar or you ca give the list parameter a list, but you can't give list a scalar. 

So save(list = c('some.variable') ... ) works, or save('some.variable', ...) also works, but save(list = 'some.variable', ...) does not work.

[John Myles White]

Can you submit a specific example of fully executable code that doesn't work so I can fix it tonight?

 -- John

[Thomas Keller]

John,

I was just working through the tutorial and noticed that the example in the tutorial does not work.
 But you are correct that putting the variable name in quotes does work.

> library(ProjectTemplate)

Loading required package: testthat

Warning message:

package ‘testthat’ was built under R version 2.15.1 

> setwd("~/Computing/R/letters")

> load.project()

Loading project configuration

Autoloading helper functions

 Running helper script: helpers.R

Autoloading packages

 Loading package: reshape2

 Loading package: plyr

 Loading package: ggplot2

 Loading package: stringr

 Loading package: lubridate

Autoloading data

 Loading cached data set: first.letter.count

 Loading cached data set: second.letter.count

 Loading data set: letters

Warning message:

package ‘stringr’ was built under R version 2.15.1 

> cache(first.letter.counts)

Error in FUN(X[[1L]], ...) : invalid first argument

> cache('first.letter.counts')

> ## no error and the object was saved in ./cache

I could have sworn the latter command also gave the error previously. My mistake.

thanks,

Tom K

[John Myles White]

Ok. To confirm: the bug is that tutorial asserts you can use an unquoted variable name, when, in fact, you need a quoted variable name?

 -- John