Adding a new Column to DF in Loop

Question

I have a loop and I am trying to create a new column to a list of lists with a constant number that is dependent on the value j (j is a number from 1 to 12). The rest of the loop works and the previous line renames the columns of the same dataframe.

for(i in 1:length(idw.list)){
  idw.output[[i]] <- list()
  for(j in 1:length(idw.list[[i]])){
    idw.output[[i]][[j]]= as.data.frame(idw.list[[i]][[j]]) 
    names(idw.output[[i]][[j]])[1:3] <- c("LON", "LAT", "MAXMEAN")
    (idw.output[[i]][[j]])[, "MONTH"] = j
}
}

I have tried this:

(idw.output[[i]][[j]])[, "MONTH"] = j

which leads to this error:

Error in (idw.output[[i]][[j]]) <- `*vtmp*` : 
  could not find function "(<-"

Right now the data looks like this:


    LON          LAT        MAXMEAN
1   11.66847    -18.04208   30.07742    
2   11.76847    -18.04208   30.07742    
3   11.86847    -18.04208   30.07742

and i would like to add the column, so that in the case j=1 (first loop):

    LON          LAT        MAXMEAN    MONTH
1   11.66847    -18.04208   30.07742    1
2   11.76847    -18.04208   30.07742    1
3   11.86847    -18.04208   30.07742    1

I would appreciate any help, thank you!

Probably there is a better way to do this. It would be helpful if you could share a reproducible example along with expected output. — Ronak Shah
– Ronak Shah, Commented Sep 15, 2019 at 13:29
Convert (idw.output[[i]][[j]])[, "MONTH"] = j to idw.output[[i]][[j]][, "MONTH"] = j. (Parenthesis are gone). Also this is quite horrible practice. I suggest creating a small example for example 2 idenical data.frames with 3 observations, with the expected result. Likely this will yield an answer with better code. — Oliver
– Oliver, Commented Sep 15, 2019 at 13:49

Ronak Shah · Accepted Answer · 2019-09-15 13:45:56Z

1

The post isn't really reproducible and this is too long for a comment but maybe you can try

for(i in seq_along(idw.list)) {
   for(j in seq_along(idw.list[[i]])) {
       names(idw.list[[i]][[j]])[1:3] <- c("LON", "LAT", "MAXMEAN")
       idw.list[[i]][[j]]["Month"] = j
     }
}

answered Sep 15, 2019 at 13:45

Ronak Shah

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