This function returns the column values of an 'Array' track in the genomic
scope specified by 'intervals'. 'slice' parameter determines which columns
should appear in the result. The columns can be indicated by their names or
their indices. If 'slice' is 'NULL' the values of all track columns are
returned.
The order inside the result might not be the same as the order of intervals.
An additional column 'intervalID' is added to the return value. Use this
column to refer to the index of the original interval from the supplied
'intervals'.
If 'file' parameter is not 'NULL' the result is saved to a tab-delimited
text file (without 'intervalID' column) rather than returned to the user.
This can be especially useful when the result is too big to fit into the
physical memory. The resulted file can be used as an input for
'gtrack.array.import' function.
If 'intervals.set.out' is not 'NULL' the result is saved as an intervals
set. Similarly to 'file' parameter 'intervals.set.out' can be useful to
overcome the limits of the physical memory.