On 2/1/2010 5:51 PM, David Winsemius wrote:
I figured this out finally. I really believe that the R help write-ups
are sorely lacking. As soon as I looked at
http://www.statmethods.net/management/merging.html, it was obvious:


    Adding Columns

To merge two dataframes (datasets) horizontally, use the *merge*
function. In most cases, you join two dataframes by one or more common
key variables (i.e., an inner join).

|# merge two dataframes by ID
total <- merge(dataframeA,dataframeB,by="ID")|

|# merge two dataframes by ID and Country
total <- merge(dataframeA,dataframeB,by=c("ID","Country")) |


    Adding Rows

To join two dataframes (datasets) vertically, use the* rbind* function.
The two dataframes *must* have the same variables, but they do not have
to be in the same order.

|total <- rbind(dataframeA, dataframeB) |

I needed to add rows, and had to use rbind. If the help for merge said
"To merge two dataframes (datasets) horizontally" I would have known
right away that it was the wrong function to use.

Thanks for the help,
Jim Rome


On Feb 1, 2010, at 5:30 PM, David Winsemius wrote:

>
> 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
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT



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