Hello everyone!
So right now I'm trying to do a data cleaning phase on text classification using Twitter dataset. But I have a problem about how to replace (or maybe remove) the URL, RT and @ character. I've read some post on the forum but I didn't understand anything :catsad:
For the URL on the dataset, I want to change the format from "https:" or "http:" to "link" (I don't know why it can't have a null value like " "). But after I executed my process using Replace operator, the result from "http://blablabla" didn't change into "link" only, but the result come out like this "linkblablabla". Maybe it has something to do with the RegEx? :catsad: I know what's RegEx but I don't how how to use and write it :catsad:
I'm really confused right now. Please help me.
This's my RapidMiner process :
<?xml version="1.0" encoding="UTF-8"?><process version="8.1.001">
<context>
<input/>
<output/>
<macros/>
</context>
<operator activated="true" class="process" compatibility="8.1.001" expanded="true" name="Process">
<process expanded="true">
<operator activated="true" class="retrieve" compatibility="8.1.001" expanded="true" height="68" name="Retrieve Dataset Skripsi" width="90" x="45" y="34">
<parameter key="repository_entry" value="Dataset Skripsi"/>
</operator>
<operator activated="true" class="nominal_to_text" compatibility="8.1.001" expanded="true" height="82" name="Nominal to Text" width="90" x="179" y="34">
<parameter key="attribute_filter_type" value="single"/>
<parameter key="attribute" value="Text"/>
</operator>
<operator activated="true" class="set_role" compatibility="8.1.001" expanded="true" height="82" name="Set Role" width="90" x="313" y="34">
<parameter key="attribute_name" value="Label"/>
<parameter key="target_role" value="label"/>
<list key="set_additional_roles"/>
</operator>
<operator activated="true" class="filter_examples" compatibility="8.1.001" expanded="true" height="103" name="Filter Examples" width="90" x="447" y="34">
<parameter key="condition_class" value="no_missing_attributes"/>
<list key="filters_list"/>
</operator>
<operator activated="true" class="remove_duplicates" compatibility="8.1.001" expanded="true" height="103" name="Remove Duplicates" width="90" x="581" y="34">
<parameter key="attribute_filter_type" value="single"/>
<parameter key="attribute" value="Text"/>
</operator>
<operator activated="true" class="replace" compatibility="8.1.001" expanded="true" height="82" name="Replace" width="90" x="715" y="34">
<parameter key="replace_what" value="(https://)"/>
<parameter key="replace_by" value="link"/>
</operator>
<connect from_op="Retrieve Dataset Skripsi" from_port="output" to_op="Nominal to Text" to_port="example set input"/>
<connect from_op="Nominal to Text" from_port="example set output" to_op="Set Role" to_port="example set input"/>
<connect from_op="Set Role" from_port="example set output" to_op="Filter Examples" to_port="example set input"/>
<connect from_op="Filter Examples" from_port="example set output" to_op="Remove Duplicates" to_port="example set input"/>
<connect from_op="Remove Duplicates" from_port="example set output" to_op="Replace" to_port="example set input"/>
<connect from_op="Replace" from_port="example set output" to_port="result 1"/>
<portSpacing port="source_input 1" spacing="0"/>
<portSpacing port="sink_result 1" spacing="0"/>
<portSpacing port="sink_result 2" spacing="0"/>
</process>
</operator>
</process>
I need your help. Thank you!
Hi @ikayunida123
There are many things you can do with regular expressions. Don't worry, what you are asking is not trivial. First of all, you have to handle a feature of regular expressions named "groups", something that not everyone is able to explain (me among these).
Look at this regex: (http|https):\/\/([\w\s\d\.]+)(\/?)(.*)
It declares four groups. The first one between the first parentheses matches http or https, then it must have the
/ (the \ is to escape the /, to avoid using something different). Then the second group comes also between parentheses, and the square brackets contain a symbol that represents every letter (\w), digit (\d) or spacing character (\s) until before the next slash. The third group is to read an optional slash (that is why it ends with a question mark), and the fourth group is for reading the rest of the URL (that .* means the next group is like the rest until EOL).
With the following setting, you can convert http://community.rapidminer.com/t5/forums/ to link:community.rapidminer.com. This might not be what you want.
Another solution is to strip the HTTP/HTTPS part. So https://community.rapidminer.com/t5/forums becomes link:community.rapidminer.com/t5/forums. This regex: (http|https):\/\/(.*) does the trick for you. It declares two groups. The first if it's http or https, the
/ (which is not a group) and all the rest. Then, in the replacement, you use link:$2 to replace the first group and the 
/ by the word "link:".
Let's say you want just the URL, no protocol nor anything. Only what comes from the DNS part. You can use this regex: (http|https):\/\/([\w\d\.\:]*)(\/?)(.*) and replace by just $2 (which makes reference to your second group), and your result will look like this:
Notice that on this, I added the \: to the second group so you can get the port too. What if I don't want the port? Well, just add \: to the third group and make it conditional, so that your regular expression is like this one: (http|https):\/\/([\w\d\.]*)(\:?|\/?)(.*). Pretty easy, huh?
No, not really. It takes a long time to master regular expressions, and you will probably wonder why would anyone care about all this magic and nonsense. The thing is that regular expressions are ugly, but if you do a lot of data preparation (like you should as a data scientist), it is much more difficult to parse stuff like URL's by actually reading the content from left to right and looking at conditions.
The simplest way to learn Regular Expressions is by practicing. You will find that these should be part of your toolkit. I always give my students this URL:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
They freeze at first, but after three or four weeks, they become little sorcerers.
Just promise me one thing: if anyone tells you that they need the regular expression for an e-mail, don't try to do it by yourself and go to http://emailregex.com/ instead. Especially if they want a regex which works with Perl. The first time I saw it, I thought it was a compressed file, or much worse, a damaged one.
Hope this helps,
Rodrigo.