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For 2021 - online Python 3 training - see ((here)).

Our plans were to retire in summer 2020 and see the world, but Coronavirus has lead us into a lot of lockdown programming in Python 3 and PHP 7.
We can now offer tailored online training - small groups, real tutors - works really well for groups of 4 to 14 delegates. Anywhere in the world; course language English.

Please ask about private 'maintenance' training for Python 2, Tcl, Perl, PHP, Lua, etc.
Dynamically formatting your results (Lua)

Scenario: You're producing a short (text) table of results and you want to keep it reasonably small - not a great deal of white space, but the data in some of your columns differs dramatically from one set of results to another. How can you do it?

Discussion: You can use your traditional "printf" type formatting in C, Perl, PHP, Python (via the % operator), Lua (string.format) and Tcl (string format) to give each field a width, but you'll need to ensure that the fields are wide enough to take the data to be placed in them every time, or accept occasional spillages when the data "busts its bank".

Solution: Parse the data for the report before you print anything out at all, and calculate the maximum width for each field for the current report. Then make up your own dynamic formatting string for use just on this occaasion. Here's an example of what I mean:

oak = {"beer","beer","beer","beer","beer","legs",
  "spilled spaghetti sauce","top","draw",
  "spit","polish","secret"}
table.sort(oak)
 
-- ====================================
 
syze = #oak[1]
for k=2,#oak do
  if syze < #oak[k] then syze = #oak[k] end
end
 
clen = #(string.format("%d",#oak));
using = "%"..clen.."d %"..syze.."s"
print ("Output format: " .. using)
 
for k,v in ipairs(oak) do
  print (string.format(using,k,v))
  end
-- ====================================


And the result:

Output format: %2d %23s
1 beer
2 beer
3 beer
4 beer
5 beer
6 draw
7 legs
8 polish
9 secret
10 spilled spaghetti sauce
11 spit
12 top


Notes: 1. If the question had been asked for web use, I would have used a browser and a table in my html to do the dynamic formatting

2. The code in the ========== section should be saved as a function for re-use later
(written 2009-11-10, updated 2009-11-11)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
U104 - Lua - Strings and the String library.
  [1744] Lua examples, Lua Courses - (2008-08-08)
  [2348] Finding literals rather than patterns in Lua - (2009-08-11)
  [2357] Checking if the user has entered a number (Lua) - (2009-08-13)
  [4274] String formatting in Lua - string.format as a wrapper for sprintf - (2014-05-07)


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