Neatly formatting results into a table

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

Would you like to produce a neat table of results, with the columns just wide enough to take the data? That sounds straightforward, but you can't output anything until you've looked through all the lines to see how long each of them will be.

I was talking about this algorithm today, and this evening I've written it up as an example of formatted printing in Ruby, and posted the complete example on our web site [here]

The trick is to do a "test" format of each of the values in each column first to find the largest, then substitute the column width into the format string for 'real' before you output the data. It's at times like this that you're really glad that a format conversion like %7.2f means "a total width of 7 columns of which 2 are after the decimal place" and not "seven figures before the decimal and 2 after"!

This technique is not appropriate if you're using a variable width font, or if you're generating output for inclusion in a web page (there are some exceptions to this latter)

(written 2010-02-01, updated 2010-02-02)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

R109 - Ruby - Strings and Regular Expressions
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [986] puts - opposite of chomp in Ruby - (2006-12-15)
  [987] Ruby v Perl - interpollating variables - (2006-12-15)
  [1195] Regular Express Primer - (2007-05-20)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1588] String interpretation in Ruby - (2008-03-21)
  [1875] What are exceptions - Python based answer - (2008-11-08)
  [1887] Ruby Programming Course - Saturday and Sunday - (2008-11-16)
  [1891] Ruby to access web services - (2008-11-16)
  [2293] Regular Expressions in Ruby - (2009-07-16)
  [2295] The dog is not in trouble - (2009-07-17)
  [2608] Search and replace in Ruby - Ruby Regular Expressions - (2010-01-31)
  [2621] Ruby collections and strings - some new examples - (2010-02-03)
  [2623] Object Oriented Ruby - new examples - (2010-02-03)
  [2980] Ruby - examples of regular expressions, inheritance and polymorphism - (2010-10-02)
  [3424] Divide 10000 by 17. Do you get 588.235294117647, 588.24 or 588? - Ruby and PHP - (2011-09-08)
  [3621] Matching regular expressions, and substitutions, in Ruby - (2012-02-23)
  [3757] Ruby - a teaching example showing many of the language features in short but useful program - (2012-06-09)
  [3758] Ruby - standard operators are overloaded. Perl - they are not - (2012-06-09)
  [4388] Global Regular Expression matching in Ruby (using scan) - (2015-01-08)
  [4505] Regular Expressions for the petrified - in Ruby - (2015-06-03)
  [4549] Clarrissa-Marybelle - too long to really fit? - (2015-10-23)

R106 - Input and Output in Ruby
  [1587] Some Ruby programming examples from our course - (2008-03-21)
  [2290] Opening and reading files - the ruby fundamentals - (2009-07-16)
  [2893] Exclamation marks and question marks on ruby method names - (2010-07-28)
  [2974] Formatting your output - options available in Ruby - (2010-09-29)
  [3429] Searching through all the files in or below a directory - Ruby, Tcl, Perl - (2011-09-09)
  [4499] Significant work - beyond helloworld in Ruby - (2015-05-27)
  [4678] Expect with Ruby - a training example to get you started - (2016-05-18)

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Some other Articles

What are Ruby Symbols?
Comparing floating point numbers - a word of caution and a solution
Defining a static method - Java, Python and Ruby
String to number conversion with error trapping in Ruby
Neatly formatting results into a table
Constants in Ruby
The Model, View, Controller architecture (MVC) - what, why and how.
Sunday Evening, City of London
Cheat Sheet - what do you need for Ruby on Rails?
Scope of variables - important to Ruby on Rails

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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