R help - Jun 2023 - Problem with filling dataframe's column

?s 21:05 de 11/06/2023, javad bayat escreveu:
> Dear R users;
> I am trying to fill a column based on a specific value in another column of
> a dataframe, but it seems there is a problem with the codes!
> The "Layer" and the "LU" are two different columns of
the dataframe.
> How can I fix this?
> Sincerely
> 
> 
> for (i in 1:nrow(data2$Layer)){
>            if (data2$Layer == "Level 12") {
>                data2$LU == "Park"
>                }
>            }
> 
> 
> 
> 
Hello,

There are two bugs in your code,

1) the index i is not used in the loop
2) the assignment operator is `<-`, not `==`


Here is the loop corrected.

for (i in 1:nrow(data2$Layer)){
   if (data2$Layer[i] == "Level 12") {
     data2$LU[i] <- "Park"
   }
}



But R is a vectorized language, the following two ways are the idiomac 
ways of doing what you want to do.



i <- data2$Layer == "Level 12"
data2$LU[i] <- "Park"

# equivalent one-liner
data2$LU[data2$Layer == "Level 12"] <- "Park"



If there are NA's in data2$Layer it's probably safer to use ?which() in 
the logical index, to have a numeric one.



i <- which(data2$Layer == "Level 12")
data2$LU[i] <- "Park"

# equivalent one-liner
data2$LU[which(data2$Layer == "Level 12")] <- "Park"


Hope this helps,

Rui Barradas

Dear Rui;
Many thanks for your email. I used one of your codes,
"data2$LU[which(data2$Layer == "Level 12")] <-
"Park"", and it works
correctly for me.
Actually I need to expand the codes so as to consider all "Levels" in
the
"Layer" column. There are more than hundred levels in the Layer
column.
If I use your provided code, I have to write it hundred of time as below:
data2$LU[which(data2$Layer == "Level 1")] <- "Park";
data2$LU[which(data2$Layer == "Level 2")] <- "Agri";
...
...
...
.
Is there any other way to expand the code in order to consider all of the
levels simultaneously? Like the below code:
data2$LU[which(data2$Layer == c("Level 1","Level 2",
"Level 3", ...))] <-
c("Park", "Agri", "GS", ...)


Sincerely




On Sun, Jun 11, 2023 at 1:43?PM Rui Barradas <ruipbarradas at sapo.pt>
wrote:
> ?s 21:05 de 11/06/2023, javad bayat escreveu:
> > Dear R users;
> > I am trying to fill a column based on a specific value in another
column
> of
> > a dataframe, but it seems there is a problem with the codes!
> > The "Layer" and the "LU" are two different columns
of the dataframe.
> > How can I fix this?
> > Sincerely
> >
> >
> > for (i in 1:nrow(data2$Layer)){
> >            if (data2$Layer == "Level 12") {
> >                data2$LU == "Park"
> >                }
> >            }
> >
> >
> >
> >
> Hello,
>
> There are two bugs in your code,
>
> 1) the index i is not used in the loop
> 2) the assignment operator is `<-`, not `==`
>
>
> Here is the loop corrected.
>
> for (i in 1:nrow(data2$Layer)){
>    if (data2$Layer[i] == "Level 12") {
>      data2$LU[i] <- "Park"
>    }
> }
>
>
>
> But R is a vectorized language, the following two ways are the idiomac
> ways of doing what you want to do.
>
>
>
> i <- data2$Layer == "Level 12"
> data2$LU[i] <- "Park"
>
> # equivalent one-liner
> data2$LU[data2$Layer == "Level 12"] <- "Park"
>
>
>
> If there are NA's in data2$Layer it's probably safer to use
?which() in
> the logical index, to have a numeric one.
>
>
>
> i <- which(data2$Layer == "Level 12")
> data2$LU[i] <- "Park"
>
> # equivalent one-liner
> data2$LU[which(data2$Layer == "Level 12")] <- "Park"
>
>
> Hope this helps,
>
> Rui Barradas
>

-- 
Best Regards
Javad Bayat
M.Sc. Environment Engineering
Alternative Mail: bayat194 at yahoo.com

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