extract_key_long: Read in inclusion in long format or variable list (in this...
In biostatUniBS/RDataXMan: Data Extraction Management

Read in inclusion in long format or variable list (in this case key.var is variable)

1	extract_key_long(research.folder, database, file, key.var)

`research.folder`	The name of research folder. See `initResearchFolder` for details on a research folder.
`database`	Name of database. Should be either `private` or `public` for flat tables, indicating whether data is stored in `public_data` or `research/[research folder]/private_data`, or the actual name of database if extracting data from a database.
`file`	The inclusion or varible list.
`key.var`	The name of variable based on which inclusion criterion is specified. Vector with multiple elements is not allowed. To have complex inclusion criteria based on multiple variables, generate one request form for each variable.