[R] Problem with filling dataframe's column

[Rui Barradas]

Às 13:18 de 11/06/2023, Rui Barradas escreveu:
> 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.

Sorry, this is not clear. I mean


This assumes that you have the new values in a vector, the vector Names 
below. The vector of values to be matched is created from the data.


Rui Barradas

> 
> 
> Values <- sort(unique(data2$Layer))
> Names <- c("Park", "Agri", "GS")
> 
> i <- match(data2$Layer, Values)
> data2$LU <- Names[i]
> 
> 
> Hope this helps,
> 
> Rui Barradas
> 
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