[R] sum two columns with same value

[Peter Ehlers]

smu wrote:
> On Sat, Oct 17, 2009 at 09:36:50AM +0200, Alfredo Alessandrini wrote:
>> Hi,
>>
>> I've two dataframe:
>>
>>> snag_totale
>>   AREA   snag_ha
>> 1    2  1.628128
>> 2    3 10.274249
>> 3    4  2.778503
>> 4    5 73.764307
>> 5    7 12.015985
>>> log_totale
>>   AREA    log_ha
>> 1    1  22.29846
>> 2    2  17.16889
>> 3    3  48.80377
>> 4    4 144.18996
>> 5    5  70.30962
>> 6    6  61.81850
>> 7    7  13.24876
>> How can I obtain a new data.frame, by the sum of value "snag_ha" +
>> "log_ha" in the same "AREA"?
> 
> 
> one way would be:
> 
> tmp <- merge(snag_totale, log_totale, by="AREA")
> tmp$sum <- tmp$snag_ha + tmp$log_ha

That will drop the missing rows in snag_totale.
Here's a variation that should work:

  tmp <- merge(snag_totale, log_totale, all = TRUE)
  tmp$Sum <- rowSums(tmp[, -1], na.rm = TRUE)
  tmp

  -Peter Ehlers

> 
> regards, 
>     stefan
> 
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