How can we take log of particular columns?

Suppose we have following data

And a function that does three things

Subsets based on what 'model' is mentioned (one of the column names of df)

Outputs decal with 3 columns

Outputs callog with the log of those values

By excluding DATE from the cold variable we can apply the log only on model and OBS_Q column

dataprep.allcal<-function(df,model){

    dfcal<<-subset(df, select=c("DATE",model, "OBS_Q"))

    #need to use the <<- operator below

    dfcallog<<-subset(df, select=c("DATE",model, "OBS_Q"))

    cols<-colnames(dfcallog)

    cols<-cols[!cols %in% 'DATE']

    dfcallog[cols] <<- log(dfcallog[cols])

  }

  dataprep.allcal(df=df,model='sac')

Output will like this