根据组条件从数据框中选择行

Question

I have a data frame which is a list of lists - a list of storms, each point of a storm is a row. One column is whether each point in the storm is over land. I'm able to work out which storms have made landfall, however I do not know how to select only those storms, ie create a new data frame of only those storms that have made landfall.

This code lets me know whether a storm has made landfall (by grouping by ID it sums the in region column (1 or 0) and if greater than 1 says it's made landfall):

land_tracks <- all_tracks[, sum(inregion) > 0, by = ID]

Gives me:

                  ID    V1
 1: 1987051906_15933  TRUE
 2: 1987060118_16870  TRUE
 3: 1987061306_18015  TRUE
 4: 1987062100_18878  TRUE
 5: 1987062918_19507 FALSE
 6: 1987070512_20168  TRUE
 7: 1987070812_20341  TRUE
 8: 1987071218_20635  TRUE
 9: 1987071412_20762  TRUE
10: 1987071606_20881  TRUE

How do I use this to go through all_tracks to find all the rows which match the ID where V1 == TRUE ?

I regularly have the issue that land_tracks has 41 rows, all_tracks has 1879 rows, and R raises an issue about recycling.

Answer 1

也许你可以在这两个表之间做一些像 INNER JOIN 这样的事情：

merge(all_tracks,land_tracks[which(land_tracks$V1== TRUE)], by = 'ID')