Regular expression gurus--help!

Ruby
1

I want all possible three letter sets for a string. Scan does this:
irb>

“abcdefghijkl”.scan(…)

>> abc

>> def

>> ghi

>> jkl

But I need:

>> abc

>> bcd

>> cde

>> def

etc.

I used to know the secret spell, but forgot it. Does anyone know how
to do this with regular expression–basically need to force the index
to advance one position rather than to the end of a match before
starting the next attempt.
Thanks in advance,
Tim

2

On Sun, Jun 21, 2009 at 4:10 PM, timr[email protected] wrote:

I used to know the secret spell, but forgot it. Does anyone know how
to do this with regular expression

Here is one way to get that result.
(But not with a regular expression)
Not all 3 letter sets but I think this is the result you are really
looking for.

str = “abcdefghijkl”
puts str.unpack(“a3X2”*(str.length-2))

#output
abc
bcd
cde
def
efg
fgh
ghi
hij
ijk
jkl

Harry

3

I fail to understand what do you mean by “all possible three-letter
sets”,
but it seems there is a method called ‘each_cons’ that does something in
the
lines of your discussion. You might find it helpful:
http://corelib.rubyonrails.org/classes/Enumerable.html#M002196

4

On 21.06.2009 10:59, Hooopo wrote:

require’enumerator’
“qwertyuiopasdfgd”.scan(/./).each_cons(3){|x,y,z| p [x,y,z].join}

Or even

“qwertyuiopasdfgd”.
scan(/./).
each_cons(3) {|a| p a.join}

Kind regards

robert

5

Am Sonntag 21 Juni 2009 09:10:37 schrieb timr:

But I need:

>> abc

>> bcd

>> cde

>> def

etc.

“abcdefghijkl”.scan(/(.)(?=(…))/).map(&:join)
=> [“abc”, “bcd”, “cde”, “def”, “efg”, “fgh”, “ghi”, “hij”, “ijk”,
“jkl”]

HTH,
Sebastian

6

On Jun 21, 4:08 pm, Harry K. [email protected] wrote:

#output

Harry

–
A Look into Japanese Ruby List in Englishhttp://www.kakueki.com/ruby/list.html

require’enumerator’
“qwertyuiopasdfgd”.scan(/./).each_cons(3){|x,y,z| p [x,y,z].join}
“qwe”
“wer”
“ert”
“rty”
“tyu”
“yui”
“uio”
“iop”
“opa”
“pas”
“asd”
“sdf”
“dfg”
“fgd”

7

Hi –

On Sun, 21 Jun 2009, Hooopo wrote:

etc.

jkl

Harry

–
A Look into Japanese Ruby List in Englishhttp://www.kakueki.com/ruby/list.html

require’enumerator’
“qwertyuiopasdfgd”.scan(/./).each_cons(3){|x,y,z| p [x,y,z].join}

Here’s another variant on this one, for 1.9:

str = “abcdefghij”
=> “abcdefghij”

str.chars.each_cons(3).map {|c| c.join }
=> [“abc”, “bcd”, “cde”, “def”, “efg”, “fgh”, “ghi”, “hij”]

David

8

I used to know the secret spell, but forgot it. Does anyone know how
to do this with regular expression–basically need to force the index
to advance one position rather than to the end of a match before
starting the next attempt.
Thanks in advance,
Tim

And another way. :slight_smile:
Again without a regular expression.

str = “abcdefghijkl”
(0…str.length-3).each {|x| p str[x…x+2]}

Harry

9

yet another solution

x.enum_for( :each_char ).each_cons( 3 ).map( &:join )

HTH
R.

–
Toutes les grandes personnes ont d’abord été des enfants, mais peu
d’entre elles s’en souviennent.

All adults have been children first, but not many remember.

[Antoine de Saint-Exupéry]

10

On Sun, Jun 21, 2009 at 9:26 PM, Sebastian
Hungerecker[email protected] wrote:

HTH,
Sebastian

I am not the OP, but thanks for that solution.
I learned more about regular expressions and relearned something about
scan.

It did not work on my machine so I changed it to this.
p “abcdefghijkl”.scan(/(.)(?=(…))/).map{|x| x.join}

Is this map(&:join) using 1.9?

Harry

11

But I need:

>> abc

>> bcd

>> cde

>> def

etc.

Ruby has so many ways. :slight_smile:

str, arr = “abcdefghijkl”, []
3.times {|f| arr << str[f…f-3].split(//)}
p arr.transpose.map{|u| u.join}

Harry

12

Hi –

On Mon, 22 Jun 2009, Harry K. wrote:

I am not the OP, but thanks for that solution.
I learned more about regular expressions and relearned something about scan.

It did not work on my machine so I changed it to this.
p “abcdefghijkl”.scan(/(.)(?=(…))/).map{|x| x.join}

Is this map(&:join) using 1.9?

Yes. In general, &obj in that position triggers the use of obj.to_proc
as the code block for the method call, and in 1.9 there’s a built-in
Symbol#to_proc method.

David

13

On Mon, Jun 22, 2009 at 3:32 AM, David A. Black[email protected]
wrote:

Is this map(&:join) using 1.9?

Yes. In general, &obj in that position triggers the use of obj.to_proc
as the code block for the method call, and in 1.9 there’s a built-in
Symbol#to_proc method.
Sorry for highjacking the thread, but I believe it served its purpose
well, already ;).

Please find a more readbale “mirror” of the following text here:
http://pastie.org/519985

Who feels with me that allowing you to do

coll.map( &:join )

but forbidding

coll.map( &:join, ", " )

is a shame.

Now it is clear that the above is not correct Ruby syntax. From my
experience very few people are fond of
the magic dot, which would solve the problem elegantly.

coll.map.join( ", " )

although in a very condensed way.

coll.map( ", ", &:join )

would be an alternative I kind of dislike.

Well burns down to

coll.map( :join, ", ")

And yes I know this is an old issue, but IIRC it has not been
discussed for some time :wink:

Cheers
Robert

–
Toutes les grandes personnes ont d’abord été des enfants, mais peu
d’entre elles s’en souviennent.

All adults have been children first, but not many remember.

[Antoine de Saint-Exupéry]

14

Robert D. wrote:

Who feels with me that allowing you to do

coll.map( &:join )

but forbidding

coll.map( &:join, ", " )

is a shame.

I think it’s pretty ugly - especially the fact that you need the
argument ", " to be passed to join, not to map, and yet it appears in
map’s argument list.

Now it is clear that the above is not correct Ruby syntax. From my
experience very few people are fond of
the magic dot, which would solve the problem elegantly.

coll.map.join( ", " )

although in a very condensed way.

That I dislike very much. What you want is to run a ‘join’ operation on
each member of the collection, but that looks like running a .map.join
on the whole collection. From that point of view,

coll.map { |c| c.join(",") }

expresses very clearly what you’re doing.

15

Hooopo wrote:

require’enumerator’
“qwertyuiopasdfgd”.scan(/./).each_cons(3){|x,y,z| p [x,y,z].join}

I see that it will not output anything if the scan is omitted but why is
that so? It seems that it does not buy us anything of value.

16

On Mon, Jun 22, 2009 at 8:32 PM, Lloyd L.[email protected]
wrote:

Hooopo wrote:

require’enumerator’
“qwertyuiopasdfgd”.scan(/./).each_cons(3){|x,y,z| p [x,y,z].join}

I see that it will not output anything if the scan is omitted but why is
that so? It seems that it does not buy us anything of value.
Because String has a somehow strange way to implement Enumerables in
1.8 and in 1.9 there is simply no String#each_cons (because String is
not an enumerable anymore)
Personally I think it was a good decision, forcing people to be clear
how they want the String to be “iterated”
as there are some possibilities
“”.enum_for( x )
x in each_byte, each_char and ???
as a short for that you have
x.bytes → Enumerator
x.chars → Enumerator
But David has already applied this technique in one of the replies, so
I might not be DRY :wink:
HTH
Robert

Cheers

–
Posted via http://www.ruby-forum.com/.

–
Toutes les grandes personnes ont d’abord été des enfants, mais peu
d’entre elles s’en souviennent.

All adults have been children first, but not many remember.

[Antoine de Saint-Exupéry]

17

I have just realized where I have made a mistake!! I’m sorry for the
fuss.

In message “Re: regular expression gurus–help!”
on 09/07/01, Nakagawa, Makoto (中川 èª ) [email protected] wrote:

“abcdefghijkl”.scan(/(.)(?=(…))/).map(&:join)
=> [“abc”, “bcd”, “cde”, “def”, “efg”, “fgh”, “ghi”, “hij”, “ijk”,
“jkl”]

I find this really interesting, but what version of Ruby is this? I
am
not able to reproduce your result.

18

In message “Re: regular expression gurus–help!”
on 09/06/21, Sebastian H. [email protected] wrote:

“abcdefghijkl”.scan(/(.)(?=(…))/).map(&:join)
=> [“abc”, “bcd”, “cde”, “def”, “efg”, “fgh”, “ghi”, “hij”, “ijk”,
“jkl”]

I find this really interesting, but what version of Ruby is this? I am
not able to reproduce your result.

$ ruby -v
ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
$ ruby1.9 -e ‘p “abcdefghijkl”.scan(/(.)((?=…))/).map(&:join)’
[“a”, “b”, “c”, “d”, “e”, “f”, “g”, “h”, “i”, “j”]

$ ruby1.9 -v
ruby 1.9.0 (2008-06-20 revision 17482) [i486-linux]
$ ruby1.9 -e ‘p “abcdefghijkl”.scan(/(.)((?=…))/).map(&:join)’
[“a”, “b”, “c”, “d”, “e”, “f”, “g”, “h”, “i”, “j”]

Or is this a feature of 1.9.1?

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