Hi,
it looks like when you read in your data.frames, you didn't tell R to
expect dates, so it treats the Date columns as factors. Judicious use of
something along these lines before doing your comparisons may help:
arr$Date <- as.Date(as.character(arr$Date),format=something)
Then again, it may be possible to do the actual merging using merge().
HTH
Stephan
James Rome schrieb:
I have two data frames. One (arr) has all arrivals to an airport for a
year, and the other (gw) has the dates and quarter hour of the day when
the weather is good. arr has a Date and quarter hour column.
names(arr)
[1] "Date" "weekday" "hour" "month" "minute"
[6] "quarter" "ICAO" "Flight" "AircraftType"
"Tail"
[11] "Arrived" "STA" "Runway" "FromTo"
"Delay"
[16] "Operator" "gw"
I added the gw column to arr and initialized it to all FALSE
names(gw)
[1] "Date" "minute" "hour" "quarter"
[5] "Efficiency.Val" "Weekly.Avg" "Arrival.Val" "Weekly.Avg.1"
[9] "Departure.Val" "Weekly.Avg.2" "Num.of.Hold" "Runway"
[13] "Weather"
First point of confusion:
gw[1,1]
[1] 1/1/09
353 Levels: 1/1/09 1/1/10 1/10/09 1/10/10 1/11/09 1/11/10 1/12/09 ... 9/9/09
Why do I get 353 levels?
I am trying to identify the quarter hours with good weather in the arr
data frame. What I want to do is to go through the rows in gw, and to
set arr$gw to TRUE if arr$Date and arr$quarter match those in the gw row.
So I tried
gooddates = function(all, good) {
la = length(all) # All the flights
lw = length(good) # The good 15-minute periods
for(j in 1:lw) {
d=good$Date[j]
q=good$quarter[j]
all[all$DateTime==d && all$quarter==q,17]=TRUE
}
}
but when I run this, I get
"Error in Ops.factor(all$DateTime, d) :
level sets of factors are different"
I know the level sets are different, that is what I am trying to find.
But I think I am comparing single elements from the data frames.
So what am I doing wrong? And there ought to be a better way to do this.
Thanks in advance,
Jim Rome
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