[R] as.factor does not work inside function

[Xiaobo Gu]

Hi Josh,

Your suggesstion works, and the following also works:
as.factor.loop <- function(df, cols){

	if (!is.null(df) && !is.null(cols) && length(cols) > 0)
	{
		for(col in cols)
    {
			df[[col]] <- as.factor(df[[col]])
		}
	}
  df
}

> df <- as.factor.loop(df, c("x","y"))
> is.factor(df[["y"]])
[1] TRUE

Thanks.

Xiaobo Gu

On Sun, Dec 11, 2011 at 10:23 AM, Joshua Wiley <jwiley.psych at gmail.com> wrote:
> Hi Xiaobo,
>
> The problem is that your function is not assigning the results to your
> data frame---df is an internatl copy made by the function.  This is
> done to prevent calling functions to have unexpected events such as
> overwriting objects in the global environment.  Anyway, I think you
> can accomplish what you want using lapply():
>
> ## your data
> df <- data.frame(x=1:5, y=2:6)
> ## apply the function, as.factor() to all the elements in the first argument
> ## and save the results in the relevant columns of df
> df["x"] <- lapply(df["x"], as.factor)
>
> ## check results
> is.factor(df[, "x"])
>
> Hope this helps,
>
> Josh
>
>
> On Sat, Dec 10, 2011 at 6:06 PM, Xiaobo Gu <guxiaobo1982 at gmail.com> wrote:
>> Hi,
>>
>> I am trying to write a function do cast columns of data frame as
>> factor in a loop, the source is :
>>
>>
>> as.factor.loop <- function(df, cols){
>>
>>        if (!is.null(df) && !is.null(cols) && length(cols) > 0)
>>        {
>>                for(col in cols)
>>    {
>>                        df[[col]] <- as.factor(df[[col]])
>>                }
>>        }
>> }
>>
>>
>> source('D:/ambertuil.r')
>> x <- 1:5
>> y <- 2:6
>> df <- data.frame(x=x, y=y)
>> as.factor.loop(df, c("x"))
>>
>> But after the function call, the df data frame does not change,
>> because
>>
>> is.factor(df[["x]])
>> FALSE
>>
>> But if I call this in R console directlly, it works
>>
>> for(col in c("x","y")){df[[col]] <- as.factor(df[[col]])}
>>
>>
>>
>> is.factor(df[["x]])
>> FALSE
>>
>>
>> Regards,
>>
>> Xiaobo Gu
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
> Joshua Wiley
> Ph.D. Student, Health Psychology
> Programmer Analyst II, Statistical Consulting Group
> University of California, Los Angeles
> https://joshuawiley.com/