How to remove hashtag content

Hello everyone,

I am new to KNIME and have a question:

I have a table which has 1000 rows and 1 column (this column data type is string), some of the content has #content, #twitter, #123, etc. I want to remove anything start with hashtag, how should I do it? I tried String Manipulation node, but the regex function inside did not take my code. Any thoughts? I used: regexReplace($Message_Original$,"#\S+", “’”)

Hi @kwjKNIME,
Welcome to community.

You need two backslashes. REGEX Not Working - #2 by amartin


Hello @kwjKNIME,

String manipulation works like a charm, why complicate our life ? :
Start & Result:

I just used “String Manipulation node (Multi column)” node (just in case your process change in the future, we never know) with :
replace($$CURRENTCOLUMN$$,"#", "")

This way, it will sparse all columns at once, easy and fast, right ?


Hi mehrdad_bgh, I used two backslashes, the code seems right, but when I click on apply, it throws an error, see the screenshot, any thoughts?

Hi SamirAbida,

I appreciate your help, but I have tried to remove the hashtag AND the content follow by it. Here is a screenshot of the error I got:

Hi @kwjKNIME and welcome to the Knime Community.

Please check out this workflow:

Inside the Text Processing metanode, there is an Extract Hashtags metanode. You can check how the hashtags are being identified and adapt it to your removal procedure. Worst case, you can do it in 2 steps:

  1. Use it to extract the hashtags to a column
  2. Do a replace using the new column - replace(original_column, new_column, “”)

Hello @mehrdad_bgh,

Sorry I didn’t understand you well.
You should use something like that which delete # + letters and numbers that follows :
Details :

  • ^ looks for everything that “start with” the following char (here the #, the\ is for escaping and avoiding errors),
  • +[a-zA-Z0-9] captures all letters or numbers following the “^#- start with #”,
  • {1,} quantifiers that look for 1 or more char.


I check the workflow that I suggested, and it looks like it’s not exactly identifying ALL hashtags, but rather only the popular ones.

So I decided to look into this.

The correct statement to identify a hashtag is actually this: #\\w+

So, you just need to use regexReplace($Message_Original$, "#\\w+", "") in a String Manipulation node:

And here’s the result:

Here’s the workflow:
Remove all hashtags.knwf (6.3 KB)

EDIT: BTW @kwjKNIME , it’s not the double slash that is creating the error you are getting. The error you are getting is because you are trying to do 2 statements (replace and regexReplace).

The correct way to apply both replace would be like this:
regexReplace(replace($Message_Original$, "’", "'"), "#\\w+", "")

Also, why are you using String Manipulation (Multi Column) if you are targeting only the column “Message_Original”? If you are going to target only 1 column, then use String Manipulation. If you are going to target multiple columns, then use “$$CURRENTCOLUMN$$” to manipulate each column via the String Manipulation (Multi Column).


Hi Samir,

I tried, but getting the following error from KNIME


Try removing the first expression. Keep only the second one.
Is it working?if so, add a second node with your first expression.



You cannot use two expressions in the same node here. As Samir implied you need to use 2 separate nodes


Thank you so much, Daniel! It is working now!

I appreciate you helping me out, Samir! I used 2 separate nodes, it is working now. :-).

1 Like

Hi @kwjKNIME , not sure why you need 2 separate nodes here. I think you missed my post. I had actually explained why it was failing, and how to run both statements in the same nodes.

I also pointed out when to use which String Manipulation node (single column vs multi column), depending on what you want to do.

Please review my post if you missed it. You don’t need to use 2 nodes.


Also, "^\\#+[a-zA-Z0-9]{1,}" identifies hashtags at the beginning of the string only, while the statement I suggested "#\\w+" identifies all hashtags in the string. Not sure which one you need.

With "#\\w+":

With "^\\#+[a-zA-Z0-9]{1,}":


Hello @bruno29a,

not quite. With the help of the quantifier {1,}, it will check all words that start with # and remove the # + what is following.

I agree that we could do well with just one node. But I’m lazy sometimes. :innocent:


Hi @SamirAbida,

Yes you are correct that adding the quantifier will allow it to find all of the characters listed in the class rather than just the first one, but I don’t think that is what @bruno29a was referring to.

I think we can be reasonably agreed that in regex (ignoring any need for double backslash in the node, as I’m just talking plain regex here)
is almost semantically the same as

in fact I think (if it included underscores)
would be semantically identical to

(I don’t know if the intention is to include underscores or not! :wink: )

But I think the main point bruno29a was making was about the use of the ^ at the beginning, so if that is included it will only match from beginning of line, as per the examples bruno29a gave, and as per the following examples:


So really, unless the request is to match only where the # appears at start of line, it shouldn’t include the ^ character.

btw…Lazy is good… I’m lazy too sometimes… when I can be bothered! :wink:


Hi @takbb,

Thank you for the time you took to explain. I see. This is indeed tricky.
And, by the way, the shorter, the better, right ? After testing, removing the ^ works better indeed !

Thanks for the guiding @bruno29a & @takbb.


Well… I like concise and elegant, but sometimes longer is clearer. Maybe it depends on the target audience, or what you are personally comfortable with.

is * better than {0,} …?
is + better than {1,} …?

is \d better than [0-9] …?
I use them interchangeably, but if I’m giving it to somebody who is new to regex, maybe I’d stick with the [0-9] initially…

\w is useful and powerful, as is \s but I confess I keep having to look them up especially if I haven’t used them in a while, as I always forget which is which between \w and \W or \s and \S
(and I often head over to to try things out)

btw @SamirAbida , I’m enjoying reading your posts. It’s great to see a new and active contributor to the forum… I was in a similar position to you back in March… none of us knows everything… we’re all on one big learning journey! :wink: