Question

I´ve asked for this on R-help one week ago, no answer until now… I´ve got multiple data.frames of gps- and temperature-data within a list. One data.frame looks like:

GPS:

       date     time     x.lat     x.lon   
1      22.05.11 13:50:37 53.57908 10.034599 
2      22.05.11 13:50:38 53.57906 10.034633 

temp:

        date     time     temp
1      22.05.11 13:50:38 21.6120
2      22.05.11 13:50:39 21.6070

So I have two lists, one with multiple gps-data.frames and one with multiple temp-dataframes. I used lapply to manipulate both lists, but can´t merge temp and gps to one big list, containing all data.frames, for only time-stamps which exists in both list, like for the above example only 13:50:38 exists in both:

GPS+temp:

       date     time    x.lat     x.lon     temp
1      22.05.11 13:50:38 53.57906 10.034633 21.6070

For the single data-frames that worked just fine with:

both <- merge(gps,temp)

For the two lists of data.frames I first tried an lapply over both lists…something like

both <- lapply(temp, gps, function(x){x <- merge(x);x})

Then I tried it with

both <- merge.list(gps,temp)

but this doesn´t work either. It just transfers the first list “gps” to both

Answer 1

Try Map:

> Map(merge, GPS, temp)
[[1]]
      date     time    x.lat    x.lon   temp
1 22.05.11 13:50:38 53.57906 10.03463 21.612

or just call mapply like Map does:

> mapply(merge, GPS, temp, SIMPLIFY=FALSE)
[[1]]
      date     time    x.lat    x.lon   temp
1 22.05.11 13:50:38 53.57906 10.03463 21.612