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digitalmars.D.learn - How do I use the Tango LineIterator.scan()?

reply Robert Kosek <robert.kosek thewickedflea.com> writes:
Hi all,

I'm working on Kata 9 of <codekata.pragprog.com>; thus far there have 
been interesting problems, but now I need scan functionality.

How does Tango's LineIterator.scan() work?  I'm still very new to D, so 
I realize this is a template function and object, but I have no idea how 
to actually use the function in this case.  Can someone give me an 
exemplary snippet or explanation on how it works?

Thanks,
Robert
Oct 13 2008
parent reply "Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:
On Mon, Oct 13, 2008 at 12:13 PM, Robert Kosek
<robert.kosek thewickedflea.com> wrote:

 Hi all,

 I'm working on Kata 9 of <codekata.pragprog.com>; thus far there have been
 interesting problems, but now I need scan functionality.

 How does Tango's LineIterator.scan() work?  I'm still very new to D, so I
 realize this is a template function and object, but I have no idea how to
 actually use the function in this case.  Can someone give me an exemplary
 snippet or explanation on how it works?

 Thanks,
 Robert


LineIterator.scan is really kind of an internal method, I'm not sure
why it's documented.  Most of the public interface to LineIterator is
in its base class, StreamIterator
(http://www.dsource.org/projects/tango/docs/current/tango.text.stream.StreamIterator.html).

There are really two ways to use a StreamIterator: the foreach way and
the next() way.

If you want to get all the lines of a stream, for instance, you can
use a foreach loop:

LineIterator lines = new LineIterator(...);
foreach(line; lines) { /* do something with each line */ }

Or, you can use the next() method:

for(auto line = lines.next(); line !is null; line = lines.next())
{ /* do something with each line */ }
Oct 13 2008
parent reply Robert Kosek <robert.kosek thewickedflea.com> writes:
Jarrett Billingsley wrote:

 LineIterator.scan is really kind of an internal method, I'm not sure
 why it's documented.

 There are really two ways to use a StreamIterator: the foreach way and
 the next() way.


That's really helpful, but what I'm trying to figure out how to do is 
grab data from a plain text file.  Columns are delimited by spaces, but 
the third column (the last) also contains spaces.  So I'm really 
searching for a char, an integer, and then a string delimited by a space.

How would I go about doing this without regex?  I know how to use regex, 
in a general sense, but I don't need it for something this simple.

Thanks for your time Jarrett.

Robert
Oct 13 2008
parent reply "Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:
On Mon, Oct 13, 2008 at 1:33 PM, Robert Kosek
<robert.kosek thewickedflea.com> wrote:

 Jarrett Billingsley wrote:

 LineIterator.scan is really kind of an internal method, I'm not sure
 why it's documented.



 There are really two ways to use a StreamIterator: the foreach way and
 the next() way.


 That's really helpful, but what I'm trying to figure out how to do is grab
 data from a plain text file.  Columns are delimited by spaces, but the third
 column (the last) also contains spaces.  So I'm really searching for a char,
 an integer, and then a string delimited by a space.

 How would I go about doing this without regex?  I know how to use regex, in
 a general sense, but I don't need it for something this simple.

 Thanks for your time Jarrett.

 Robert


In that case, once you have the line that you got from the
LineIterator, you can split it up using methods found in
tango.text.Util.  You can use the locate() function to find the first
space.  You can then set it to start at a certain position, so that
you can get the position of the second space after it.

import tango.text.Util;
...
// using line as the line of text.
auto firstSpace = line.locate(' '); // syntactic sugar for locate(line, ' ')
auto secondSpace = line.locate(' ', firstSpace + 1);
auto firstCol = line[0 .. firstSpace];
auto secondCol = line[firstSpace + 1 .. secondSpace];
auto thirdCol = line[secondSpace + 1 .. $]; // $ means line.length

// now you can convert the columns as you please
Oct 13 2008
next sibling parent Robert Kosek <robert.kosek thewickedflea.com> writes:
Jarrett Billingsley wrote:

 You can use the locate() function to find the first
 space.  You can then set it to start at a certain position, so that
 you can get the position of the second space after it.


Thank you very much Jarrett, this was just what I needed.  I got the 
whole thing working now. :)

Thanks,
Robert
Oct 13 2008
prev sibling parent reply =?UTF-8?B?QWxleGFuZGVyIFDDoW5law==?= writes:
Jarrett Billingsley wrote:

 import tango.text.Util;
 ...
 // using line as the line of text.
 auto firstSpace = line.locate(' '); // syntactic sugar for locate(line, ' ')
 auto secondSpace = line.locate(' ', firstSpace + 1);
 auto firstCol = line[0 .. firstSpace];
 auto secondCol = line[firstSpace + 1 .. secondSpace];
 auto thirdCol = line[secondSpace + 1 .. $]; // $ means line.length
 
 // now you can convert the columns as you please


auto columns = line.split(" ");
auto firstCol = columns[0];
auto secondCol = columns[1];
// ... that’s a tad shorter. :P
Oct 13 2008
next sibling parent Robert Kosek <robert.kosek thewickedflea.com> writes:
Alexander Pánek wrote:

 auto columns = line.split(" ");
 auto firstCol = columns[0];
 auto secondCol = columns[1];
 // ... that’s a tad shorter. :P


Quite so, Alexander, and that's what I switched to in my code.  I 
refactored what I had and switched to commas, just in case someone uses 
whitespace to pad things. ;-)

And if you know what exercise 9 is on the site, you have variable input. 
  Which does make it a fun experience.  My constructor just takes the 
line and parses it, so it's quite convenient.

I wound up with:

 this(char[] line) {
   auto parts = split(line, ",");

   this.sku = parts[0][0];
   this.price = Integer.parse(parts[1]);
   this.hasSpecial = parts.length >= 3;

   if(this.hasSpecial) {
     auto parts2  = split(parts[2], " for ");
     this.s_qty   = Integer.parse(parts2[0]);
     this.s_price = Integer.parse(parts2[1]);
   }
 }


And I use the LineInput object in the parent class to read and iterate 
through the lines.

I must say that I like D and the Tango library. =)

Cheers,
Robert
Oct 14 2008
prev sibling parent reply "Jarrett Billingsley" <jarrett.billingsley gmail.com> writes:
On Mon, Oct 13, 2008 at 10:28 PM, Alexander P=E1nek
<alexander.panek brainsware.org> wrote:

 Jarrett Billingsley wrote:

 import tango.text.Util;
 ...
 // using line as the line of text.
 auto firstSpace =3D line.locate(' '); // syntactic sugar for locate(line=




, '

 ')
 auto secondSpace =3D line.locate(' ', firstSpace + 1);
 auto firstCol =3D line[0 .. firstSpace];
 auto secondCol =3D line[firstSpace + 1 .. secondSpace];
 auto thirdCol =3D line[secondSpace + 1 .. $]; // $ means line.length

 // now you can convert the columns as you please


 auto columns =3D line.split(" ");
 auto firstCol =3D columns[0];
 auto secondCol =3D columns[1];
 // ... that's a tad shorter. :P


The third column can have spaces.  This will split on them too.  Not
to mention line.split() will allocate a new array every time it's
called ;)
Oct 14 2008
parent =?UTF-8?B?QWxleGFuZGVyIFDDoW5law==?= writes:
Jarrett Billingsley wrote:

 On Mon, Oct 13, 2008 at 10:28 PM, Alexander Pánek
 <alexander.panek brainsware.org> wrote:

 Jarrett Billingsley wrote:

 import tango.text.Util;
 ...
 // using line as the line of text.
 auto firstSpace = line.locate(' '); // syntactic sugar for locate(line, '
 ')
 auto secondSpace = line.locate(' ', firstSpace + 1);
 auto firstCol = line[0 .. firstSpace];
 auto secondCol = line[firstSpace + 1 .. secondSpace];
 auto thirdCol = line[secondSpace + 1 .. $]; // $ means line.length

 // now you can convert the columns as you please


 auto columns = line.split(" ");
 auto firstCol = columns[0];
 auto secondCol = columns[1];
 // ... that's a tad shorter. :P


 
 The third column can have spaces.  This will split on them too.  Not
 to mention line.split() will allocate a new array every time it's
 called ;)


Nittypickybulubulub! It is shorter in code, qed. ;P
Oct 14 2008