[Octave-bug-tracker] [bug #38149] regexp: doesn't return empty tokens -- they just disappear

[Nicholas Jankowski]

Update of bug #38149 (project octave):

                Priority:              5 - Normal => 3 - Low                

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Follow-up Comment #17:

this appears to still be an issue in curred dev branch for v8.0.0

in the comment #0 code, the 'this works' example matches between octave v8.0.0
and matlab 2022a. The second two work in matlab but in Octave produce:

error: t(2): out of bound 1 (dimensions are 1x1)


for Rik's test script in comment #13, matlab 2022a currently produces:


>> te = regexp ('abc', 'abc(z?)', 'tokenExtents');
celldisp (te)
te{1} =
     4     3
>> te = regexp ('abce', '((a)(z)?b(c)(z*))(z)?(e)?', 'tokenExtents');
celldisp (te)
te{1} =
     1     3
     4     3
     4     4
>> [T, TE, NM] = regexp (sprintf('%s','John Davis\nRogers, James'),
'(?<first>\w+)\s+(?<last>\w+)|(?<last>\w+),\s+(?<first>\w+)', 'tokens',
'tokenExtents', 'names');
>> celldisp (T)
T{1}{1} =
John
T{1}{2} =
Davis
T{2}{1} =
nRogers
T{2}{2} =
James
>> celldisp (TE)
TE{1} =
     1     4
     6    10
TE{2} =
    12    18
    21    25
>> NM(1).first
ans =
    'John'
>> NM(1).last
ans =
    'Davis'
>> NM(2).first
ans =
    'James'
>> NM(2).last
ans =
    'nRogers'


while octave produces:


>> te = regexp ('abc', 'abc(z?)', 'tokenExtents');
>> celldisp (te)
te{1} =

   4   3

>> te = regexp ('abce', '((a)(z)?b(c)(z*))(z)?(e)?', 'tokenExtents')
;
>> celldisp (te)
te{1} =

   1   3
   1   1
   3   3
   4   3
   4   4

>> [T, TE, NM] = regexp (sprintf('%s','John Davis\nRogers, James'),
'(?<first>\w+)\s+(?<last>\w+)|(?<last>\w+),\s+(?<first>\w+)', 'token
s', 'tokenExtents', 'names');
>> celldisp (T)
T{1}{1} =

John

T{1}{2} =

Davis

T{2}{1} =

nRogers

T{2}{2} =

James

>> celldisp (TE)
TE{1} =

    1    4
    6   10
                                                                    
TE{2} =

   12   18
   21   25

>> NM(1).first
ans = John
>> NM(1).last
ans = Davis
>> NM(2).first
ans = James
>> NM(2).last
ans = nRogers


where the only difference appears in the 2nd "celldisp (te)" line. 


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