[R] Problem with filling dataframe's column

[Rui Barradas]

Às 22:54 de 11/06/2023, javad bayat escreveu:
> 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 using sapo.pt> wrote:
> 
>> Às 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
>>
> 
> 
Hello,

You don't need to repeat the same instruction 100+ times, there is a way 
of assigning all new LU values at the same time with match().
This assumes that you have the new values in a vector.


Values <- sort(unique(data2$Layer))
Names <- c("Park", "Agri", "GS")

i <- match(data2$Layer, Values)
data2$LU <- Names[i]


Hope this helps,

Rui Barradas