It looks like that blog link is broken since it is from 2013. However, I was able to track down the code. You will need to copy and paste this into IDL: and name it colsort.pro:

========================================================
; docformat = 'rst'
;+
; :description:
; Applies SORT (ascending order) to a selected column of a two-dimensional
; array, then applies this sort to all the columns of the array. (It's like
; doing a column sort in Excel.)
;
; :params:
; array: in, required, type=numeric
; A two-dimensional numeric array.
; column_index: in, required, type=integer
; The column index over which sorting is performed.
;
; :keywords:
; reverse_sort: in, optional, type=boolean
; Set this keyword to do a reverse sort (descending order) on the
; elements of the selected column.
;
; :author:
; Mark Piper, ITT VIS, 2009
;
; :version:
; $Id: colsort.pro 182 2009-11-03 21:44:28Z mpiper $
;-
function colsort, array, column_index, reverse_sort=rsort
compile_opt idl2
on_error, 2

info = size(array, /structure)

; Test dimensions of input array.
if info.n_dimensions ne 2 then $
message, 'Input array must have two dimensions.'

; Ensure the sorting index is within a valid range.
if n_elements(column_index) eq 0 then $
message, 'Must pass a column index for sorting.'
n_columns = info.dimensions[0]
_column_index = (column_index > 0) < (n_columns-1)

; Sort the desired column.
col_sort_index = sort(array[_column_index,*])
if keyword_set(rsort) then $
col_sort_index = reverse(col_sort_index)

; Apply the sort to each column of the array.
sorted_array = array
for i=0, n_columns-1 do $
sorted_array[i,*] = (array[i,*])[col_sort_index]

return, sorted_array
end


;+
; Example main. Examine the results in the Console.
;-
a = round(randomu(123, 5, 6) * 20.0)
sort_index = 1
b = colsort(a, sort_index, /reverse_sort)
print, 'Original array:'
print, a
print
print, 'Column index to sort on: ', sort_index
print
print, 'Sorted (reverse) array:'
print, b
end