;+
; Select data from the given io object and return the array of
; matching indices.
;
; Currently, the selection criteria are passed directly to the io
; class's get_index function via the _EXTRA parameter.  Eventually, a
; more specific detailed interface will be found here.
;
; See the line index's
; <a href="../toolbox/io/line_index__define.html#_LINE_INDEX::search_index">search_index</a> or
; continuum index's <a href="../toolbox/io/cntm_index__define.html#_CNTM_INDEX::search_index">search_index</a>
; for the full set of parameters that are available.
;
; @param io_object {in}{optional}{type=sdfits io object} The io object
; on which the selection is performed
;
; @keyword count {out}{optional}{type=integer} The number of matches found.
;
; @returns an array of indicies.  Returns a value of -1 if no match
; was found.
;
; @version $Id: select_data.pro,v 1.4 2005/05/18 17:06:40 bgarwood Exp $
;-
FUNCTION select_data, io_object, count=count, _EXTRA=ex
    compile_opt idl2

    result = -1
    count = 0

    if (io_object->is_data_loaded()) then begin
        result = io_object->get_index(_EXTRA=ex)
        if result[0] ne -1 then count = n_elements(result)
    endif else begin
        message, 'There is no data to select from', /info
    endelse

    return, result
END