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How do you do regular expressions at the character level?

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Tom Bernand
Tom Bernand 2023-10-25
编辑： Walter Roberson 2023-10-31
Hello all,
I am trying to find words in a text with a set of rules and then extract them. I am looking for words with a certain structure. The words themselves have different lengths and letters.
for example:
term_1 = "TER";
term_2 = "ZTnE";
term_3 = "ZEnP";
...
Since I have a lot of terms, I tried to create a pattern with character-level rules. To do this, I split up the terms and always looked to see which character could occur at which position in the string.
For the simple example above:
1st place:
seg_1 = '[TZ]'
2nd place:
seg_2 = '[ET]'
3rd digit:
seg_3 = '[nR]'
4th digit:
seg_4 = '[EP]'
seg = seg_1 + seg_2 + seg_3 + seg_4;
result = extract(term_2, seg)
This now works for a term with the same length, but term_1 is not recognised.
Therefore, I have now made the following adjustment and declared the 4th seg as optionalPattern:
seg_4 = optionalPattern("E" | "P");
This is how the extraction works now. However, terms are now also extracted that skip an optionalPattern in the meantime.
Does anyone have any other ideas on how I can easily and safely include terms of different lengths?
Thank you very much!

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采纳的回答

Walter Roberson
Walter Roberson 2023-10-25
编辑：Walter Roberson 2023-10-25
Ran in:
"+" on character vectors is not a pattern operation.
seg_1 = '[TZ]'
seg_1 = '[TZ]'
seg_2 = '[ET]'
seg_2 = '[ET]'
seg = seg_1 + seg_2
seg = 1×4
182 153 174 186
char(seg)
ans = '¶□®º'
p_1 = characterListPattern('TZ')
p_1 = pattern
Matching: characterListPattern("TZ")
p_2 = characterListPattern('ET')
p_2 = pattern
Matching: characterListPattern("ET")
p_1 + p_2
ans = pattern
Matching: characterListPattern("TZ") + characterListPattern("ET")
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Walter Roberson
Walter Roberson 2023-10-29
编辑：Walter Roberson 2023-10-31
In terms of your original patterns, 'ZT E' would require that seg_3 match space instead of [nR]
To allow space instead of one of the characters, include space in the [] if you are using regexp
seg_1 = "[ TZ]"
seg_2 = "[ ET]"
seg_3 = "[ nR]"
seg_4 = "[ EP]";
seg = seg_1 + seg_2 + seg_3 + seg_4;
result = regexp(term_2, seg, 'match');
If you want to more generally include "whitespace" (such as tab) then instead of putting a space in the [], use \s such as "[\sTZ]"
Tom Bernand
Tom Bernand 2023-10-31
Perfect, that worked out great.
I must have been thinking in a complicated way.
Thank you very much!

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