[R] add specific fields in for loop

[Rui Barradas]

Às 19:39 de 15/11/2022, Kai Yang escreveu:
> Hello Rui,
> Yes, it should be the one I want. I modified the code as:
> 
> for(i in grep("data", names(df))) {
>    try2.un$ab2 <-
>      ifelse(grepl("ab2",  [i]),   [i], NA)
> }
> 
> But I got error message:
> Error: unexpected '[' in:
> "  try2.un$ab2 <-
>      ifelse(grepl("ab2",["
> 
> I think I use [i] in a wrong way. Do you have any suggestion?
> Thanks,
> Kai   On Tuesday, November 15, 2022 at 10:54:08 AM PST, Rui Barradas <ruipbarradas using sapo.pt> wrote:
>   
>   Às 16:18 de 15/11/2022, Kai Yang via R-help escreveu:
>> Hi Team,
>> I can write a for loop like this:
>> for (i in columns(df)){
>>      ......
>> }
>>
>> But it will working on all column in dataframe df. If I want to work on some of specific fields (say: the fields' name content 'date'), how should I modify the for loop? I changed the code below, but it doesn't work.
>> for (i in columns(df) %in% 'date' ){
>>      .....
>> }
>>
>>
>> Thank you,
>> Kai
>>
>>      [[alternative HTML version deleted]]
>>
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>> and provide commented, minimal, self-contained, reproducible code.
> Hello,
> 
> Something like this?
> 
> 
> for(i in grep("date", names(df))) {
>    #
> }
> 
> 
> Hope this helps,
> 
> Rui Barradas
> 
>    
Hello,


For what I understand of the problem any of the two below does what the 
posted code seems to be trying to do. The first is better, no ifelse.


for(i in grep("data", names(df))) {
   is.na(try2.un$ab2) <- !grepl("ab2", df[[i]])
}

for(i in grep("data", names(df))) {
   try2.un$ab2 <- ifelse(grepl("ab2", df[[i]]), df[[i]], NA)
}


Hope this helps,

Rui Barradas