I’m trying to write a little script to rename my mp3s I started with this:
mp3DirName = ARGV[0]
mp3Dir = Dir.new(mp3DirName)
$fileNames = mp3Dir.entries
#this filters out things that aren’t .mp3s
$fileNames.each { |x| if !(x =~ /.*mp3$/)
$fileNames.delete(x)
end
}#end each block
$fileNames.each { | fileName | print fileName + “\n” }
which should print the names of mp3s found the the directory given at
the command line. As near as I can tell the regex test is working right,
but $fileNames.delete(x) doesn’t seem to be doing anything. I can do
$fileNames.delete("."); and that removes the entry “.” from the list. I
haven’t a clue why this doesn’t just work, but I’m guessing/hoping it’s
some idiosyncracy of ruby that I just don’t know about. Thanks again guys 
Jeremy Gregorio
gunvalk@cox.net
Hi Jeremy,
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
To make things straightforward, however, you should have used
“delete_if” instead of using “each” and “delete”:
mp3DirName = ARGV[0]
mp3Dir = Dir.new(mp3DirName)
$fileNames = mp3Dir.entries
#this filters out things that aren’t .mp3s
$fileNames.delete_if { |x| x !~ /.*mp3$/} # this is modified
$fileNames.each { | fileName | print fileName + “\n” }
Regards,
Bill
···
============================================================================
Jeremy Gregorio gunvalk@cox.net wrote:
I’m trying to write a little script to rename my mp3s I started with this:
mp3DirName = ARGV[0]
mp3Dir = Dir.new(mp3DirName)
$fileNames = mp3Dir.entries
#this filters out things that aren’t .mp3s
$fileNames.each { |x| if !(x =~ /.*mp3$/)
$fileNames.delete(x)
end
}#end each block
$fileNames.each { | fileName | print fileName + “\n” }
which should print the names of mp3s found the the directory given at
the command line. As near as I can tell the regex test is working right,
but $fileNames.delete(x) doesn’t seem to be doing anything. I can do
$fileNames.delete(“.”); and that removes the entry “.” from the list. I
haven’t a clue why this doesn’t just work, but I’m guessing/hoping it’s
some idiosyncracy of ruby that I just don’t know about. Thanks again guys 
Jeremy Gregorio
gunvalk@cox.net
Dir is more powerful than that:
Dir.chdir ARGV[0]
puts Dir.glob(‘*.mp3’).join(“\n”)
···
Jeremy Gregorio (gunvalk@cox.net) wrote:
I’m trying to write a little script to rename my mp3s I started with this:
mp3DirName = ARGV[0]
mp3Dir = Dir.new(mp3DirName)
$fileNames = mp3Dir.entries
#this filters out things that aren’t .mp3s
$fileNames.each { |x| if !(x =~ /.*mp3$/)
$fileNames.delete(x)
end
}#end each block
$fileNames.each { | fileName | print fileName + “\n” }
–
Eric Hodel - drbrain@segment7.net - http://segment7.net
All messages signed with fingerprint:
FEC2 57F1 D465 EB15 5D6E 7C11 332A 551C 796C 9F04
And for those who haven’t used C++ … what is the issue? And does it
explain why the simpler method I was planning to suggest doesn’t work
either?
My suggestion was going to be:
fileNames = mp3Dir.entries.collect {|f| f =~ /.*mp3$/}
or something much like it. But no go.
···
On Thu, Oct 03, 2002 at 07:44:12AM +0900, William Djaja Tjokroaminata wrote:
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
–
Matt Gushee
Englewood, Colorado, USA
mgushee@havenrock.com
Oops! Never mind. ‘collect’ was the wrong method. This works:
fileNames = mp3Dir.entries.find_all {|f| f =~ /.*mp3$/}
···
On Thu, Oct 03, 2002 at 07:50:02AM +0900, Matt Gushee wrote:
On Thu, Oct 03, 2002 at 07:44:12AM +0900, William Djaja Tjokroaminata wrote:
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
And for those who haven’t used C++ … what is the issue? And does it
explain why the simpler method I was planning to suggest doesn’t work
either?
My suggestion was going to be:
fileNames = mp3Dir.entries.collect {|f| f =~ /.*mp3$/}
or something much like it. But no go.
–
Matt Gushee
Englewood, Colorado, USA
mgushee@havenrock.com
Cool, thanks. I haven’t programmed ruby (or any OO language) in a
while, so I forgot about that little bit. Thanks again.
Jeremy Gregorio
gunvalk@cox.net
Well, I don’t know how to explain it easily without using the concept of
pointer. For the expert Ruby programmers, can someone help here?
Regards,
Bill
···
===========================================================================
Matt Gushee mgushee@havenrock.com wrote:
On Thu, Oct 03, 2002 at 07:50:02AM +0900, Matt Gushee wrote:
On Thu, Oct 03, 2002 at 07:44:12AM +0900, William Djaja Tjokroaminata wrote:
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
And for those who haven’t used C++ … what is the issue?
Well, I do have a general idea of what pointers are, though I can’t
speak for other non-C++ programmers. Can’t promise to understand, but
you might try your pointerful explanation.
···
On Thu, Oct 03, 2002 at 08:44:26AM +0900, William Djaja Tjokroaminata wrote:
Well, I don’t know how to explain it easily without using the concept of
pointer. For the expert Ruby programmers, can someone help here?
–
Matt Gushee
Englewood, Colorado, USA
mgushee@havenrock.com
Hello William,
Thursday, October 03, 2002, 3:44:26 AM, you wrote:
use a concept of index when we delete element currently indexed by
iterator, this index will point to next element and when we increment
that index, we will just skip one element totally
···
Well, I don’t know how to explain it easily without using the concept of
pointer. For the expert Ruby programmers, can someone help here?
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
–
Best regards,
Bulat mailto:bulatz@integ.ru
Well, that’s simple enough. I was expecting something more esoteric. So
does this mean that at the implementation level there’s really no
difference between
stuff.each
and
for (int i = 0; i < stuff.length(); i++) {
?
···
On Thu, Oct 03, 2002 at 02:21:32PM +0900, Bulat Ziganshin wrote:
use a concept of index when we delete element currently indexed by
iterator, this index will point to next element and when we increment
that index, we will just skip one element totally
Well, I don’t know how to explain it easily without using the concept of
pointer. For the expert Ruby programmers, can someone help here?
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
–
Matt Gushee
Englewood, Colorado, USA
mgushee@havenrock.com
Hi Bulat,
See,
... this index will *point* to next element ...
There I think we use a concept of pointer :). Fortunately, Matt grasped
it easily.
Regards,
Bill
···
===========================================================================
Bulat Ziganshin bulatz@integ.ru wrote:
Hello William,
Thursday, October 03, 2002, 3:44:26 AM, you wrote:
use a concept of index when we delete element currently indexed by
iterator, this index will point to next element and when we increment
that index, we will just skip one element totally
Well, I don’t know how to explain it easily without using the concept of
pointer. For the expert Ruby programmers, can someone help here?
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
–
Best regards,
Bulat mailto:bulatz@integ.ru
If you ever used C++, then you would have known the issue of deleting
an
element while you are traversing the container using an iterator.
Well, that’s simple enough. I was expecting something more esoteric. So
does this mean that at the implementation level there’s really no
difference between
stuff.each
and
for (int i = 0; i < stuff.length(); i++) {
?
–
Matt Gushee
For an array, perhaps, but it’s not true for a generic iterator. Not
everything that supports :each also supports :length.
Or : for that matter.
Gavin
···
From: “Matt Gushee” mgushee@havenrock.com
Hello Matt,
Thursday, October 03, 2002, 9:44:54 AM, you wrote:
If you ever used C++, then you would have known the issue of deleting an
element while you are traversing the container using an iterator.
Well, that’s simple enough. I was expecting something more esoteric. So
does this mean that at the implementation level there’s really no
difference between
stuff.each
and
for (int i = 0; i < stuff.length(); i++) {
definitely yes! iterator is a method of ABSTRACTING this cycle, hiding
implementation details from class user. but internally it runs the
same cycle
···
–
Best regards,
Bulat mailto:bulatz@integ.ru
Hi,
Both Java and C++ have iterators, but usually in C++ books the iterators
are accompanied by examples on how to write them in C, and therefore it is
crystal clear there the issues that may surface.
Regards,
Bill
···
=======================================================================
Bulat Ziganshin bulatz@integ.ru wrote:
Well, that’s simple enough. I was expecting something more esoteric. So
does this mean that at the implementation level there’s really no
difference between
stuff.each
and
for (int i = 0; i < stuff.length(); i++) {
definitely yes! iterator is a method of ABSTRACTING this cycle, hiding
implementation details from class user. but internally it runs the
same cycle
Hello William,
Thursday, October 03, 2002, 5:25:42 PM, you wrote:
in ruby books there is the same examples. may be difference is that
the ruby programmers may not read this examples in order to start
using iterators
···
Both Java and C++ have iterators, but usually in C++ books the iterators
are accompanied by examples on how to write them in C, and therefore it is
crystal clear there the issues that may surface.
Well, that’s simple enough. I was expecting something more esoteric. So
does this mean that at the implementation level there’s really no
difference between
stuff.each
and
for (int i = 0; i < stuff.length(); i++) {
–
Best regards,
Bulat mailto:bulatz@integ.ru