[R] how to chage values in data frame to NA iside a function

[Petr Pikal]

Thank you for your answers. It works OK but my real question is 
why my  function behaves differently used on vector and data 
frame (or matrix or list).  

I attached a full version below with some foo data, but basically 
the function  returns the correct index if applied correctly on any 
type (list, data frame, matrix,  vector) but it changes values of 
operand only if operand is a vector. 

Why please? 

On 21 Feb 2003 at 10:23, Spencer Graves wrote: 

> Thomas Blackwell's solution will also work if dropout(df$y) returns a 
> logical vector of length = length(df$y).  This also allows more 
> general conditions, e.g., 
>  
>    select1 <- df[,1] > 0 
>    select2 <- (select1) & (dr[,2] > 0) 
>  
>    df[select2, "y"] <- NA	 
>  
> Spencer Graves 
>  
> Thomas W Blackwell wrote: 
> > Petr  - 
> >  
> > Does your function return "index" or return "y" after modifying y ? 
> > In the email, it looks as though it returns "index".  If so, the 
> > following should work: 
> >  
> >  
> >>df$y[ dropout(df$y) ] <- NA 
> >  
> >  
> > -  tom blackwell  -  u michigan medical school  -  ann arbor  - 
> >  
> >  
> >  
> > On Fri, 21 Feb 2003, Petr Pikal wrote: 
> >  
> >  
> >>Dear all 
> >> 
> >>I have a function in which I would like to change some values to NA 
> >>according to some condition. 
> >> 
> >>dropout<-function(y, nahr=FALSE,...) { 
> >> 
> >><some stuff for computing an index> 
> >> 
> >>if (nahr) y[index]<<-NA 
> >>invisible(index) 
> >> 
> >>} 
> >> 
> >>in case y is a vector all works OK but if it is a part of data frame 
> >>by calling 
> >> 
> >>dropout(df$y) or dropout(df[,number]) no change is done. 
> >> 
> >>Please can you help me what is wrong with my code? 
> >> 
> >>By the way 
> >> 
> >>idx<-dropout(df$y) 
> >>df$y[idx]<-NA 
> >> 
> >>works OK 
> >> 
> >>Thanks a lot beforehand 
> >> 
> >>Best regards. 
> >> 
> >>Petr Pikal 


#foo data 

x<-seq(0,100,.1) 
y<-sin(x)+rnorm(length(x),mean=0,sd=1) 
y1<-y-c(rep(0,200),exp(x[20:50]),rep(0,770)) 
y<-y1+50 
y<-y*(y>0) 
y[600:700]<-0 
df<-data.frame(y) 
mat<-as.matrix(df) 
mylist<-as.list(df) 

#vector 

plot(x,y) 
ddd<-dropout(y) 
points(x[ddd],y[ddd],col=2) 
ddd<-dropout(y,nahr=T) 
plot(x,y) 
rm(ddd) 

#data frame 

plot(x,df$y) 
ddd<-dropout(df$y) 
points(x[ddd],df$y[ddd],col=2) 
ddd<-dropout(df$y,nahr=T) 
plot(x,df$y) 
rm(ddd) 

#matrix 

plot(x,mat[,1]) 
ddd<-dropout(mat[,1]) 
points(x[ddd],mat[ddd,1],col=2) 
ddd<-dropout(mat[,1],nahr=T) 
plot(x,mat[,1]) 
rm(ddd) 

#list 

plot(x,mylist$y) 
ddd<-dropout(df$y) 
points(x[ddd],mylist$y[ddd],col=2) 
ddd<-dropout(mylist$y,nahr=T) 
plot(x,mylist$y) 

#this is full function 

dropout<-function(y,span=21, mez=NULL, p=0.99995, 
nahradit=FALSE, ...) { 

### this part is just computing the logical index vector with length 
= length(y)  ### and TRUE values where dropout occurs 

#kontrola licheho spanu 
if(span/2-span%/%2<.4|span<2) span<-
ceiling(span+floor(1/span)+.1) 

n<-length(y) 
s<-span%/%2 


idx1<-y==0 
prumer<-median(y[!idx1],na.rm=T) 

if (is.null(mez))   
{ 
mez<-mad(y[!idx1],na.rm=T) 
dm<-prumer-mez*qnorm(p) 
hm<-prumer+mez*qnorm(p) 
} else { 

dm<-prumer-mez 
hm<-prumer+mez 
} 


idx2<-y<dm 
idx3<-y>hm 

idx<-as.logical(idx1+idx2+idx3) 
z <- embed(idx,span) 
rowSums(z) 
length(rowSums(z)) 
sumy<-rowSums(z)>0 
index<-c(rep(sumy[1],s),sumy,rep(sumy[n-span+1],s)) 

### index is a returned logical vector and it is OK 

if (nahradit) y[index]<<-NA 
### this is the ghastly line which does not work as I expected :-( 

invisible(index) 

} 


Thank you 

Best regardsPetr Pikal
petr.pikal at precheza.cz
p.pik at volny.cz