[R] Column naming mystery

[Werner Wernersen]

Hi,

I hope somebody could help me explain what seems
mysterious to me? 

I use this line on a dataframe ae:
summaryBy(total_inflated+total~gr1, data=ae, FUN=sum,
na.rm=T)

and it returns 3 columns as expected and columns "gr1"
and "total_inflated.sum"are correct but the
"total.sum" column consists of only zeros which is not
correct. The same happens when I rename the
"total_inflated" to "total.inflated" or
"totalinflated" but not when I rename it to
"ttotal_inflated". In the latter case I get the
correct result also for the "total.sum" column.

Could anyone explain the rules for the column naming
to me?

Thank you very much in advance!
  Werner


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