equivalent of excel "sumif"

R-help,

 I have two data frames df1 and df2:

 >head(df1)

  lgdcm 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
     0 0 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0
     1 0 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0
     2 0 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0
     3 0 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0
     4 0 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0
     5 0 0 0 0 0 0 0 0 0 0  0  0  0  0  0  0
 ...
 ...

 > head(df2)

  lgdcm  0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
       34 NA NA  1 NA NA NA NA NA NA NA NA NA NA NA NA NA
       36 NA NA  1 NA NA NA NA NA NA NA NA NA NA NA NA NA
       40 NA NA  1  1 NA NA NA NA NA NA NA NA NA NA NA NA
       41 NA NA NA NA  3 NA NA NA NA NA NA NA NA NA NA NA
       42 NA NA NA NA  7 NA NA NA NA NA NA NA NA NA NA NA
       43 NA NA NA  1  6 NA NA NA NA NA NA NA NA NA NA NA
 ....
 ....

 I want to fill up the columns of df1 (0,1,2,,,,15)
 with columns from df2 (0,1,2,,,,15) with column 'lgdcm' as the
 criterion for matching.

 There is a function in excel which does this type of thing, something
 like:
 SUMIF(range,criteria,sum_range)

 Can anyone help with this?

 Thanks in advance.