[R] Conditional Variable Assignment

[Hosack, Michael]

Hi everyone,

Once again I am stuck with a problem I can't seem to 
figure out. I suppose this learning curve levels off 
eventually, lol. I am learning on my own with absolutely
 no background in programming, so if I seem to request 
help a lot it's not because I am seeking others to do
 the work for me. I need to assign one of two arrival 
times to the 'ARRIVE' variable of my dataframe, and 
I want a value assigned only to the first element of 
each 'MM' by 'DD' variable grouping. The value used 
(either 0700 or 1430) will be conditional on the value
 in the 'TOD' variable, such that if 'TOD' == 1, 
'ARRIVE'<-0700, and if 'TOD'==2, 'ARRIVE'<-1430. I 
want the remaining three 'MM' by 'DD' values for 
each unique grouping to remain "NA" for now, because 
I intend to calculate them later. I have tried 
ifelse statements with ddply, for loops, etc. to 
no avail. Any help would be greatly appreciated.

Thank you,

Mike
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