Regex (preg_match in php) : last groups in the output array don't work correctly

Question

With this pattern:

(how is\s)?(the\s)?(weather)\s?((on)\s)?(today|tomorrow|sunday|monday|tuesday|wednesday|thursday|friday|saturday|sunday|this week)?(\s(in)\s(.*)\s?(on)?\s?(today|tomorrow|sunday|monday|tuesday|wednesday|thursday|friday|saturday|sunday|this week)?)?

This is what I'm trying to capture

Input : how is the weather on tuesday in vienna

output :

array(10
0   =>  how is the weather on tuesday in vienna
1   =>  how is 
2   =>  the 
3   =>  weather
4   =>  on 
5   =>  on
6   =>  tuesday
7   =>   in vienna
8   =>  in
9   =>  vienna
)

Here, I can extract day and location from array[6] and array[9]

Input : how is the weather in vienna on tuesday

output :

array(10
0   =>  how is the weather in vienna on tuesday
1   =>  how is 
2   =>  the 
3   =>  weather
4   =>  
5   =>  
6   =>  
7   =>  in vienna on tuesday
8   =>  in
9   =>  vienna on tuesday
)

But here, the location and day are captured as a whole in array[9]. I want it to capture day and location in different elements. Is there anything wrong with the grouping in regex pattern?

I didn't understand your question can you give some sample data and your expected output? — Federico Piazza
– Federico Piazza, Commented May 30, 2016 at 2:42
i don't understand what you are trying to achieve but I did a bit of modification and it works giving the output..writing too long regex with so many optional groups is not too good — rock321987
– rock321987, Commented May 30, 2016 at 2:46
There isn't anything wrong with capturing timeframe and location in a grouping regex, but it would seem more valuable to capture the timeframe in one capture group, and the location in a separate capture group. This way the values can be used immediately in your program. — Ro Yo Mi
– Ro Yo Mi, Commented May 30, 2016 at 3:02

Ro Yo Mi · Accepted Answer · 2016-05-30 03:12:17Z

1

Description

I recommend using optional lookaheads to seek out and find the location or timeframe if they exist.

Regular expression visualization

This regular expression will do the following:

capture group 1 always gets the timeframe if it exists in the string
capture group 2 always gets the location if it exists in the string
allows the location and timeframe to appear in any order in the string

Example

Live Demo

https://regex101.com/r/rN9hG2/1

Sample text

weather on sunday
weather on sunday in vienna
weather in vienna
weather in vienna on sunday

Sample Matches

[0][1] = sunday
[0][2] = 

[1][1] = sunday
[1][2] = vienna

[2][1] = 
[2][2] = vienna

[3][1] = sunday
[3][2] = vienna

Explanation

NODE                     EXPLANATION
----------------------------------------------------------------------
  (?=                      look ahead to see if there is:
----------------------------------------------------------------------
    (?:                      group, but do not capture (optional
                             (matching the most amount possible)):
----------------------------------------------------------------------
      .*?                      any character except \n (0 or more
                               times (matching the least amount
                               possible))
----------------------------------------------------------------------
      on                       'on'
----------------------------------------------------------------------
      \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
      (                        group and capture to \1:
----------------------------------------------------------------------
        today                    'today'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        tomorrow                 'tomorrow'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        sunday                   'sunday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        monday                   'monday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        tuesday                  'tuesday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        wednesday                'wednesday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        thursday                 'thursday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        friday                   'friday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        saturday                 'saturday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        sunday                   'sunday'
----------------------------------------------------------------------
       |                        OR
----------------------------------------------------------------------
        this week                'this week'
----------------------------------------------------------------------
      )                        end of \1
----------------------------------------------------------------------
    )?                       end of grouping
----------------------------------------------------------------------
  )                        end of look-ahead
----------------------------------------------------------------------
  (?=                      look ahead to see if there is:
----------------------------------------------------------------------
    (?:                      group, but do not capture (optional
                             (matching the most amount possible)):
----------------------------------------------------------------------
      .*?                      any character except \n (0 or more
                               times (matching the least amount
                               possible))
----------------------------------------------------------------------
      in                       'in'
----------------------------------------------------------------------
      \s                       whitespace (\n, \r, \t, \f, and " ")
----------------------------------------------------------------------
      (                        group and capture to \2:
----------------------------------------------------------------------
        [a-z]+                   any character of: 'a' to 'z' (1 or
                                 more times (matching the most amount
                                 possible))
----------------------------------------------------------------------
      )                        end of \2
----------------------------------------------------------------------
    )?                       end of grouping
----------------------------------------------------------------------
  )                        end of look-ahead
----------------------------------------------------------------------

edited May 30, 2016 at 3:12

answered May 30, 2016 at 2:49

Ro Yo Mi

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10 Comments

Lord Stiltskin Over a year ago

This works perfectly. I'm still trying to understand the pattern though. Thank you so much

Ro Yo Mi Over a year ago

Think of it like this the (?=.*?......) plants its feet and uses binoculars to look ahead into the string to see if the string contains the desired text.

Ro Yo Mi Over a year ago

Capture group zero is always populated. When you added the (?:....) you are asking the regular expression engine to match a value which if it exists will be returned. I see that you added ? to the end of them but this only means the string is optional.

Ro Yo Mi Over a year ago

Of course this would fail to match the string In vienna on saturday what will the weather be like. So I'd just add (?=(?:.*?weather)?) which would look forward into the string to verify the word weather is contained in the string somewhere. This way the word weather, the time period, and location can appear in any order.

Ro Yo Mi Over a year ago

The regular expression engine will attempt to step through your source string one character at a time, then when it encounters a lookahead, the engine looks forward to see if the following string matches a pattern. This page has a much better explanation that I can provide here.

|

Federico Piazza · Accepted Answer · 2016-05-30 02:55:45Z

Capture all words

If I understood your question well, to capture those words then you can use a regex like this:

(\w+)\s+(\w+)\s+(\w+)(?:\s+(\w+)\s(\w+))?

Regular expression visualization

Regex demo

Match information

MATCH 1
1.  [3-10]  `weather`
2.  [11-13] `on`
3.  [14-20] `sunday`
MATCH 2
1.  [25-32] `weather`
2.  [33-35] `on`
3.  [36-42] `sunday`
4.  [43-45] `in`
5.  [46-52] `vienna`
MATCH 3
1.  [57-64] `weather`
2.  [65-67] `in`
3.  [68-74] `vienna`
MATCH 4
1.  [79-86] `weather`
2.  [87-89] `in`
3.  [90-96] `vienna`
4.  [97-99] `on`
5.  [100-106]   `sunday`

Capture only your words in bold

On the other hand, if you want to capture your words in bold, then you can remove some capturing groups like below regex:

\w+\s+\w+\s+(\w+)(?:\s+\w+\s(\w+))?

Regular expression visualization

Regex demo

Match information

MATCH 1
1.  [14-20] `sunday`
MATCH 2
1.  [36-42] `sunday`
2.  [46-52] `vienna`
MATCH 3
1.  [68-74] `vienna`
MATCH 4
1.  [90-96] `vienna`
2.  [100-106]   `sunday`

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Regex (preg_match in php) : last groups in the output array don't work correctly

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Capture all words

Capture only your words in bold

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Your Answer

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Capture all words

Capture only your words in bold

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