[R] Beginer data.frame

[Stephan Kolassa]

Hi Jean-Baptiste,

two points:

1) Your variable "df" is a *local* variable which you define in your 
function myfunc(), so it is not known outside myfunc(). When you ask 
is.data.frame(df), R looks at the global definition of df - which is the 
density function of the F distribution. To make your function run 
(especially interactively) will require a major rewrite.

2) Generally, using variable names that are already used as R objects 
(like "df" in your example) is a bad idea. For an example of the 
problems you can run into, see 1) above.

3) Loops are not "the R way". Depending on what you want to do with the 
subset of your data.frame, you may want to do something like this:

x.df[substr(x.df$Code,1,1)=="R",]

Look at ?substr to learn more - this function is "vectorized", meaning 
that it takes a vector input and returns a vector output. Look at 
section 2.7 in "An introduction to R".

Good luck!
Stephan


Jean-Baptiste Combes schrieb:
> Hello,
> 
> I use R 2.10, and I am new in R (I used to use SAS and lately Stata), I am
> using XP.
> 
> I have a data which has a data.frame format called x.df (read from a csv
> file). I want to take from this data observations for which the variable
> "Code" starts with an "R". I took all the Code and put them into a vector
> vec<-grep("R[A-Z][A-Z]",x.df$Code,value=TRUE)
> 
> Then I created a function that is supposed to take all the lines in the my
> data x.df for which "Code" equals one value of "vec". See the code below
> where I created a loop to do that.
> 
>> myfunc<-function(data,var2,var1)
> + {
> + i=1
> + while (i<632){
> + line<-subset(data,var2==var1[i])
> + if (i==1){
> + df<-line
> + df<-data.frame(df)
> + }
> + else {
> + line<-data.frame(line)
> + df<-rbind(df,line)
> + }
> + i<-i+1
> + }
> + fix(df)
> + }
> 
> The results of my program higly depend on the few last lines of the program.
> If I put "fix(df)", as above, the function opens a window with my data and
> it seems a sensible results (I have not checked in details but I barely have
> what I am suppose to get).
>> myfunc<-function(data,var2,var1)
> ...
> + }
> + df<-data.frame(df)
> + print(is.data.frame(df))
> + }
>> myfunc(x.df,x.df$Code,vec)
> [1] TRUE
>> print(is.data.frame(df))
> [1] FALSE
> 
> In the case above I ask whether or not the "df" is a data.frame and the
> answer is true, when the program has ended, I ask again and the answer is
> false.
> 
> Could anyone tell me what to do to get this data and could anyone tell me
> why those differences in the results?
> 
>> as.data.frame(df)
> Erreur dans as.data.frame.default(df) :
>   impossible de convertir automatiquement la classe  "function" en un
> tableau de données (data.frame)
> 
> 	[[alternative HTML version deleted]]
> 
> 
> 
> ------------------------------------------------------------------------
> 
> ______________________________________________
> 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.