dataframe does not work inside of a function - r

Question

When trying to generate a data.frame inside of a function, found that when calling the function, despite everything apparently worked well outside of the function, the data.frame was not generated.
Anybody could tell me how is this possible?
Species=c("a","b","c")
data=data.frame(Species)
df=data.frame(matrix(nrow=length(levels(data$Species)),ncol=43))
rm(df)
f<-function(data)
{
df=data.frame(matrix(nrow=length(levels(data$Species)),ncol=43))
}
f(data)
In my Rstudio no data.frame is generated when calling the function f!
> sessionInfo()
R version 2.14.1 (2011-12-22)
Platform: x86_64-pc-mingw32/x64 (64-bit)
locale:
[1] LC_COLLATE=English_Australia.1252
LC_CTYPE=English_Australia.1252
LC_MONETARY=English_Australia.1252
[4] LC_NUMERIC=C LC_TIME=English_Australia.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] plyr_1.7.1 maptools_0.8-14 lattice_0.20-0 foreign_0.8-48
geosphere_1.2-26
[6] rgdal_0.7-8 outliers_0.14 XML_3.9-4.1 PBSmapping_2.62.34
dismo_0.7-14
[11] raster_1.9-58 sp_0.9-93
loaded via a namespace (and not attached):
[1] grid_2.14.1 tools_2.14.1

Answer 1

This should not be surprising. You haven't specified anywhere in the function what the function should return. This can be done the same way you display an object that you have created at the command prompt in R: type the name of the object. Alternatively, you can use return().
In other words, modify your function as follows (I've changed "df" to "mydf" and "data" to "mydata" to avoid any potential conflicts with base R functions):
f <- function(mydata)
{
mydf = data.frame(matrix(nrow=length(levels(data$Species)), ncol=43))
mydf
## Or, more explicitly
## return(mydf)
}
You can now run it using f(data). However, note that this will just display the output, not assign it to an object. If you wanted it assigned to an object ("mydf", for example) you need to use mydf <- f(data).
There is another option, use <<- in your function.
f <- function(mydata)
{
mydf <<- data.frame(matrix(nrow=length(levels(data$Species)), ncol=43))
## uncomment the next line if you want to *display* the output too
## mydf
}
> rm(mydf)
> ls(pattern = "mydf")
character(0)
> f(data) ## No ouput is displayed when you run the function
> ls(pattern = "mydf")
[1] "mydf"