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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.
Nothing beats Perl to solve a data manipulation requirement quickly

OK - I admit it. It might be slightly out of fashion but I still love Perl for that quick hack script which is a one-off data manipulation need.

I have two files - the first containing records of who signed our pledge for an appropriate TransWilts train service last year, and another containing records in the same format for those who have signed this year, and I wanted a list of people who haven't reconfirmed their support.

Here's a "break the rules of good programming" piece of code that I slapped together in a few minutes ...

open (FH,"08.cooked");
while (<FH>) {
  chop;
  $key = lc;
  $signed{$key} = 1;
  $lastyear{$key} = 1;
  }
  
open (FH,"09.cooked");
while (<FH>) {
  chop;
  $key = lc;
  $signed{$key} = 2;
  }
  
foreach $previous (keys %signed) {
  # last year only
  if ($signed{$previous} == 1) {
    print "$previous\n" ;
    $awaited += 1;
    }
  if ($signed{$previous} == 2) {
    # this year only
    $newcomer += 1 if (! $lastyear{$previous}) ;
    # this year and last year
    $both += 1 if ($lastyear{$previous}) ;
    }
  }
print ("$awaited last year only\n");
print ("$both both years\n");
print ("$newcomer new this year\n");


... and after a couple of syntax errors and a couple of validation tests, it ran for me and fulfilled its job.

Coding rules broken.

1. Cut and paste the file read code - un-necessary duplication
2. Poorly (un-named!) variable - use of $_
3. Combined data and report output of STDOUT needed cutting about later
4. Lack of descriptive comment block

but job done, and I can move on with my once-only result set and take a look through the output, considering and acting on the data provided which was the purpose in the first place.

P.S. Had I been working from database tables, a left join looking for orphan records would have let me do the whole data thing as a one-liner:

mysql> select pledges.email from pledges left join pledge09 on pledges.email = pledge09.email where pledge09.pid is NULL;

with slight modifications for each of the counts


We offer courses in both Perl Programming and in MySQL. One of the most popular pages on our web site explains the difference between the types of join in MySQL and how to extract all the different data combinations you might want.
(written 2009-04-14, updated 2009-04-16)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
P772 - Practical Example - Perl in use
  [2047] Small Web Server in Perl - (2009-02-18)
  [2657] Want to do a big batch edit? Nothing beats Perl! - (2010-03-01)

P669 - Perl - Data Munging
  [597] Storing a regular expression in a perl variable - (2006-02-09)
  [1316] Filtering and altering Perl lists with grep and map - (2007-08-23)
  [1509] Extracting information from a file of records - (2008-01-16)
  [1947] Perl substitute - the e modifier - (2008-12-16)
  [2702] First and last match with Regular Expressions - (2010-04-02)
  [3335] Practical Extraction and Reporting - (2011-06-26)
  [3707] Converting codons via Amino Acids to Proteins in Perl - (2012-04-25)
  [3764] Shell, Awk, Perl of Python? - (2012-06-14)
  [4620] Perl 6 - a Practical Extraction and Reporting example! - (2016-01-11)


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Bigger and better this year!
Learning about Lurchers
Patterns in street names
Javascript - move cursor over image to change a different image.
Nothing beats Perl to solve a data manipulation requirement quickly
Wiltshire - where everybody matters
Call in the professionals!
Weeding out old phone numbers
We have lost a regular business guest
Building down expectations
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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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