Where is grep?

Ruby
1

Hello,

I tried to grep from a string, but got wrong.

irb(main):010:0* x = “hello world baby girl”
=> “hello world baby girl”
irb(main):011:0>
irb(main):012:0*
irb(main):013:0* x.grep(/hello/)
NoMethodError: undefined method grep' for "hello world baby girl":String from (irb):13 from /usr/bin/irb:12:in’

where shall ‘grep’ method come from?

thanks~

2

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Grep is not defined on Ruby 1.9-Strings.

It was on Ruby 1.8-Strings, but only because they were belonging to
the group of objects that mixed in Enumerable.

There, grep behaves like this (line by line):

x = “hello world baby girl”
x.grep(/hello/)
#=> [“hello world baby girl”]
x = “hello\nworld\nbaby\ngirl”
x.grep(/hello/)
#=> [“hello\n”]

The same can be done in Ruby 1.9 by just splitting the String
beforehand. Arrays are Enumerable and thus
still have grep:

x = “hello\nworld\nbaby\ngirl”
x.split("\n").grep(/hello/)
#=> [“hello”]

Note the absence of the line-break which might be intended or not :).

Regards,
Florian G.

On Nov 27, 2009, at 11:26 PM, Ruby N. wrote:

girl":String
from (irb):13
from /usr/bin/irb:12:in `’

where shall ‘grep’ method come from?

thanks~

Florian G.

smtp: [email protected]
jabber: [email protected]
gpg: 533148E2

-----BEGIN PGP SIGNATURE-----
Version: GnuPG/MacGPG2 v2.0.12 (Darwin)

iEYEARECAAYFAksQlbgACgkQyLKU2FMxSOJ3eQCgkltVUHDzm4jPszZ1xh8Yn0Up
kGEAoKhK7atdiHhiKTT1l3F2fL0YK1bo
=qtur
-----END PGP SIGNATURE-----

3

Thanks, that sounds be more reasonable, b/c I like to grep from an
array not a string (yes perl does this).

btw, why 0/0 got failed but 0.0/0.0 seems valid?

irb(main):144:0> v=0/0
ZeroDivisionError: divided by 0
from (irb):144:in /' from (irb):144 from /usr/bin/irb:12:in ’

irb(main):145:0> v=0.0/0.0
=> NaN

2009/11/28 Florian G. [email protected]:

4 
    from (irb):144
    from /usr/bin/irb:12:in `<main>'

irb(main):145:0> v=0.0/0.0
=> NaN

It’s the difference betweeen floating point and integer arithmetic.
When working with integers all results must be valid integers, whereas
floating point can represent NaN (Not a Number), negative zero,
and infinity and negative infinity:

irb(main):001:0> 1.0/0.0
=> Infinity
irb(main):002:0> -0.0
=> -0.0
irb(main):003:0> 0.0/-0.0
=> NaN
irb(main):004:0> -1.0/0.0
=> -Infinity
irb(main):005:0>

See Floating-point arithmetic - Wikipedia for more information.

5

Hi –

On Sat, 28 Nov 2009, Florian G. wrote:

x = “hello\nworld\nbaby\ngirl”

Note the absence of the line-break which might be intended or not :).

I would probably do this in 1.9:

string.lines.grep(/pattern/)

where lines returns an enumerator.

David

6

On Nov 28, 2009, at 3:57 AM, David A. Black wrote:

I would probably do this in 1.9:

string.lines.grep(/pattern/)

where lines returns an enumerator.

David

Jep, there is always room to improve. It also maps better to the old
behaviour where you were basically grepping #each_line.

Thanks,
Florian

7

On 11/28/2009 08:27 AM, David A. Black wrote:

where lines returns an enumerator.
Why not just string.scan(/pattern/) ?

Kind regards

robert

8

On 11/28/2009 05:35 PM, Rick DeNatale wrote:

On Sat, Nov 28, 2009 at 11:10 AM, Robert K.
[email protected] wrote:

On 11/28/2009 08:27 AM, David A. Black wrote:

irb(main):001:0> a = “abe\nbob\nfred\njim”
=> “abe\nbob\nfred\njim”
irb(main):002:0> a.scan(/b/)
=> [“b”, “b”, “b”]
irb(main):003:0> a.lines.grep(/b/)
=> [“abe\n”, “bob\n”]

a.lines.grep does the same thing that a.grep would do in 1.8, a.scan does not.

Stupid me, of course! Thanks for the quick enlightenment. I somehow
had assumed the text the OP was ultimately interested in was that
matched by the expression. But that assumption is not covered by the
posting.

Cheers

robert

9

On Sat, Nov 28, 2009 at 11:10 AM, Robert K.
[email protected] wrote:

Arrays are Enumerable and thus
string.lines.grep(/pattern/)

where lines returns an enumerator.

Why not just string.scan(/pattern/) ?

Not the same thing

using 1.9

irb(main):001:0> a = “abe\nbob\nfred\njim”
=> “abe\nbob\nfred\njim”
irb(main):002:0> a.scan(/b/)
=> [“b”, “b”, “b”]
irb(main):003:0> a.lines.grep(/b/)
=> [“abe\n”, “bob\n”]

a.lines.grep does the same thing that a.grep would do in 1.8, a.scan
does not.

–
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Twitter: http://twitter.com/RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale