{"id":11803,"date":"2020-10-15T18:14:19","date_gmt":"2020-10-15T22:14:19","guid":{"rendered":"https:\/\/blogs.mathworks.com\/pick\/?p=11803"},"modified":"2020-10-23T12:42:24","modified_gmt":"2020-10-23T16:42:24","slug":"r2020b-pattern-new-way-to-regular-express","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/pick\/2020\/10\/15\/r2020b-pattern-new-way-to-regular-express\/","title":{"rendered":"R2020b: pattern (new way to regular express)"},"content":{"rendered":"

Jiro<\/a>'s Pick this week is the new pattern matching<\/a> capabilities that were added in the newest release, R2020b.<\/p>

I've always had a love-hate relationship with regular expressions<\/a>. It's a powerful technique for string searching. It's powerful, but it's quite complicated as well. The fact that there are books on regular expressions goes to show that it is not a trivial technique to completely master. We have Picked a couple of entries related to regular expressions in the past, such as a regular express cheat sheet<\/a> and a regular expression builder app<\/a>.<\/p>

With R2020b, there is a whole new way of searching and modifying text. It involves a much simpler method of building pattern expressions using simple functions.<\/p>

\"\" <\/p>

Let's look at an example. Here is a string vector.<\/p>

str = [\"When I joined MathWorks, the version of MATLAB was R2006a.\"<\/span>\r\n  \"When I moved to Japan, r2014a had just been released.\"<\/span>\r\n  \"Now, six years later, the current version is R2020B.\"<\/span>];\r\n<\/pre>
Let's say that I want to extract all of the MATLAB releases from the text. All I need to do is search for patterns starting with \"R\", followed by 4 numbers, followed by \"a\" or \"b\".<\/p>
pat = \"R\"<\/span> + digitsPattern(4) + (\"a\"<\/span>|\"b\"<\/span>)\r\n<\/pre>
pat = \r\n  pattern\r\n  Matching:\r\n    \"R\" + digitsPattern(4) + (\"a\" | \"b\")\r\n<\/pre>
To allow case insensitive search,<\/p>
pat = caseInsensitivePattern(pat)\r\n<\/pre>
pat = \r\n  pattern\r\n  Matching:\r\n    caseInsensitivePattern(\"R\" + digitsPattern(4) + (\"a\" | \"b\"))\r\n<\/pre>
Now we simply extract!<\/p>
extract(str, pat)\r\n<\/pre>
ans = \r\n  3×1 string array\r\n    \"R2006a\"\r\n    \"r2014a\"\r\n    \"R2020B\"\r\n<\/pre>
For reference, if we were to do this with regular expressions,<\/p>
regexp(str, \"[Rr]\\d{4}[aAbB]\"<\/span>, \"match\"<\/span>)\r\n<\/pre>
ans =\r\n  3×1 cell array\r\n    {[\"R2006a\"]}\r\n    {[\"r2014a\"]}\r\n    {[\"R2020B\"]}\r\n<\/pre>
You be the judge as to which one is easier to understand.<\/p>
Take a look at this page<\/a> for more examples. Patterns will not be able to completely replace regular expressions, but not to worry! You can use regexpPattern<\/tt><\/a> to match regular expressions.<\/p>\r\n
<\/p>\r\nEDIT: Check out one of the comments<\/a> below to see a slightly more complicated example.\r\n
<\/p>\r\n
Comments<\/b><\/p>
Give it a try and let us know what you think here<\/a>.<\/p>