Fixed missing prefix on stops.txt$parent_station on merge_gtfs() method

[gmatosferreira]

According to GTFS official documentation, stops.txt has a column parent_station that references a stops.txt$stop_id. However, the method gtfstools::merge_gtfs() only considers the columns that end with _id when applying the prefix parameter, which is generating an invalid parent_station column in the merged GTFS when this column exists.

gtfstools/R/merge_gtfs.R

Line 161 in 6bb51d8

id_cols <- names(dt)[(grepl("_id$", names(dt)))]

GTFS documentation for stops.txt parent_station column

Example of output for TCB GTFS (https://backend.tcbarreiro.pt/download-gtfs) with a prefix equal to the agency_id, where we can see that only the stop_id was changed, while the parent_station remain unchanged.

With a simple refactoring to include parent_station in the id_cols filter fixes this.

[gmatosferreira]

I just validated the changes locally using remotes::install_github("gmatosferreira/gtfstools", ref="patch-2") and this change fixes the problem I report.

[rafapereirabr]

thanks, @gmatosferreira . nice catch and simple fix !