A<-airquality
B<-data.frame(Month=unique(A$Month),col=c("Ozone","Solar.R", "Wind", "wind","Solar.R"))

> head(A)
   Ozone Solar.R Wind Temp Month Day
1    41     190  7.4   67     5   1
2    36     118  8.0   72     5   2
3    12     149 12.6   74     5   3
4    18     313 11.5   62     5   4
5    NA      NA 14.3   56     5   5
6    28      NA 14.9   66     5   6
> B
            Month        col
1               5       Ozone
2               6     Solar.R
3               7        Wind
4               8        wind
5               9     Solar.R

> head(A)
   Ozone Solar.R Wind Temp Month Day  ADDED
1    41     190  7.4   67     5   1    41
2    36     118  8.0   72     5   2    36
3    12     149 12.6   74     5   3    12
4    18     313 11.5   62     5   4    18
5    NA      NA 14.3   56     5   5    NA
6    28      NA 14.9   66     5   6    28

> tail(A)
    Ozone Solar.R Wind Temp Month Day ADDED
148    14      20 16.6   63     9  25    20
149    30     193  6.9   70     9  26   193
150    NA     145 13.2   77     9  27   145
151    14     191 14.3   75     9  28   191
152    18     131  8.0   76     9  29   131
153    20     223 11.5   68     9  30   223

for(i in 1:nrow(B))
{
  j<-A$Month==B$Month[i]
  k<-subset(A, select=B$col[i])[j,]
  A$ADDED[j]<-k
}