From: Brian Adkins <lojicdotcom@...>
Date: 2008-01-12T13:20:01+09:00
Subject: Re: Multiline (block) CSV file processing

On Jan 10, 5:21 pm, Phil Rhoades <p...@pricom.com.au> wrote:
> On Fri, 2008-01-11 at 06:47 +0900, Phil Rhoades wrote:
> > On Fri, 2008-01-11 at 04:19 +0900, Brian Adkins wrote:
> > > def block_extractor file, fields,
> > >     splitter = lambda {|line| line.split }
> > >   while !file.eof
> > >     result = []
> > >     fields.each do |field|
> > >       line = file.readline
> > >       result << splitter.call(line.chomp)[field-1] if field
> > >     end
> > >     yield result
> > >   end
> > > end
>
> > > File.open("data.txt", "r") do |file|
> > >   block_extractor(file, [1,2,5,10,12]) do |fields|
> > >     puts fields.join(' ')
> > >   end
> > > end
>
> > Thanks! - now I just need to work out how that actually works and then
> > work out how I can modify it to use command line parameters.
>
> I apologise for replying to my own post but I have had a look at this
> and read up about Procs and Lambdas and I can sorta see what you are
> doing but would you be so kind as to elaborate on the code a bit? - I
> think other people would find it useful as well . .

I'd be glad to. What question do you have?

> Also, to generalise the code further, how would you select two of more
> fields from each line?

Well, this is very much a toy/example program, so I wouldn't build on
it too much. There is a cost and a benefit to generalization, so it
might be worthwhile to spend some time thinking about how general you
need the function to be.

A simple way to select two or more fields from each line would be to
change from:

[a, b, ...]

to:

[ [a1, a2, ...] [b1, b2, ...] ... ]

or possibly use a hash with the key being a block-relative line
number, and the value being a list of field numbers. Or you may want
an external specification of the fields to extract - kind of like HTML
templating in reverse.


Brian Adkins