;+
; NAME:
;    WRITE_CSV
;
; PURPOSE:
;    Writes a comma-separated-variables (CSV) file from a CSV-style
;    structure as read in by READ_CSV.
;
; CATEGORY:
;    I/O
;
; CALLING SEQUENCE:
;    WRITE_CSV, Filename, Csvstruct
;
; INPUTS:
;    Filename:  Name of CSV file to write to.
;
;    Csvstruct: Structure containing data. If there are N fields, then
;               the first N tags in the structure must be the data fields
;               followed by 2 longs containing NROWS and NCOLS.
;
; OUTPUTS:
;    Writes out a comma-separated-variables (CSV) file with a one-line header
;    of the form '# COL1,COL2,COL3....'.
;
; EXAMPLE:
;    Write back a CSV structure:
;
;    IDL> HELP, /STRUCT, Galstruct
;    ** Structure <8237564>, 6 tags, length=80, data length=80, refs=1:
;        NAME            STRING    Array[2]
;        OBJID           ULONG64   Array[2]
;        RA              DOUBLE    Array[2]
;        DEC             DOUBLE    Array[2]
;        NROWS           LONG                 2
;        NCOLS           LONG                 4
;    IDL> WRITE_CSV, 'galaxies.csv', Galstruct
;
; MODIFICATION HISTORY:
;    Written by:  Jeremy Bailin
;    11 June 2008 Public release in JBIU
;-
pro write_csv, filename, csvstruct

on_error, 0

header_names = tag_names(csvstruct)

openw, lun, filename, /get_lun
printf, lun, '# ', FORMAT='(A,$)'
for i=0L,csvstruct.ncols-2 do printf, lun, header_names[i], FORMAT='(A,",",$)'
printf, lun, header_names[csvstruct.ncols-1]

for i=0L,csvstruct.nrows-1 do begin
  strline=''
  for j=0L,csvstruct.ncols-1 do begin
    case size(csvstruct.(j), /type) of
      7 : strline += string(csvstruct.(j)[i], FORMAT='(%"%s",$)')
      5 : strline += string(csvstruct.(j)[i], FORMAT='(G0.10,$)')
      15: strline += string(csvstruct.(j)[i], FORMAT='(I0,$)')
    endcase
    if j ne csvstruct.ncols-1 then strline += string(',', FORMAT='(A1,$)')
  endfor
  printf, lun, strline
endfor

close, lun
free_lun, lun

end