Re: [R] merging data frames gives all NAs

[David Winsemius]

On Feb 1, 2010, at 5:16 PM, James Rome wrote:
Dear kind R helpers,

I have a vector of runway names in rwy  ("31R", "31L",...  the  
number is user selectable)
arrgnd is a data frame with data for all flights and all runways,  
with a Runway column.
I am trying to subset arrgnd into a dat frame for each selected  
runway, and then combine them back together using the following code:

for (j in 1:nr) {    # nr = number of user-selected runways

Safer would be:

 for (j in seq_along(rwy) {

   ar4rw = arrgnd[arrgnd$Runway==rwy[j],]

Clearer would be :

        ar4rw <- subset(arrgnd, Runway=j) # and I think the NA line's  
will also disappear.


   if (j == 1) {
       arrw = ar4rw
   }
   else {
       arrw = merge(arrw, ar4rw)
   }
}

You really should give us something like:

dput(rwy)
dput( head(arrgnd, 10) )

but, the merge step gives me a data frame with all NAs. In addition,  
ar4rw always gets a row with NAs at the start, which I do not  
understand. There are no rows with all NAs in the arrgnd data frame.
> ar4rw[1:2,]  # first time through for 31R
       DateTime       Date month hour minute quarter weekday IATA  
ICAO Flight
NA <NA> <NA>    NA   NA     NA      NA      NA <NA> <NA> <NA>
529 1/1/09 21:46 2009-01-01     1   21     46      87       5   TA   
TAI TAI570
   AircraftType   Tail  Arrived   STA Runway     FromTo Delay
NA <NA> <NA> <NA> <NA> <NA> <NA>    NA
529         A320 N496TA 21:46:58 22:30    31R MSLP /KJFK     0
                      Operator            dq gw
NA <NA> <NA> NA
529 TACA INTERNATIONAL AIRLINES 2009-01-01 87  1

> ar4rw[1:2,]   # second time through for 31L
       DateTime       Date month hour minute quarter weekday IATA  
ICAO Flight
NA <NA> <NA>    NA   NA     NA      NA      NA <NA> <NA> <NA>
552 1/1/09 23:03 2009-01-01     1   23      3      92       5   AA   
AAL  AAL22
   AircraftType   Tail  Arrived   STA Runway    FromTo  
Delay          Operator
NA <NA> <NA> <NA> <NA> <NA> <NA>    NA <NA>
552         B762 N329AA 23:03:35 23:10    31L LAX  /JFK     0  
AMERICAN AIRLINES
              dq gw
NA <NA> NA

But after the merge, I get all NAs. What am I doing wrong?

The data layout gets mangled and I cannot tell what rows are being  
matched to what. Use dput to convey an unambiguous, and easily  
replicated example.

Thanks,
Jim Rome

552 2009-01-01 92  1

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David Winsemius, MD
Heritage Laboratories
West Hartford, CT

______________________________________________
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.