find number and add and operation character (java, knime)

Question

I am working on knime with a string replacer node and have to add an mathematical operation sign (multiplication, '*') behind a digit number (within a string cell). I find the numbers with the (java-based) regular expression

((?:\d+\.)?\d+ )

I tried to add the multiplication operation by adding the replacement text

((?:\d+\.)?\d+)\*

But the replacement now creates something like:

to be replaced:

1.456 substance

actually replaced by:

((?:\d+\.)?\d+)\*substance

But needed is:

1.456*substance

How can I modify the replacement text to get the needed output or what is the proper approach?

Thank you.

Answer 1

Note that when you search for the text, you are using a regular expression pattern, and when replacing, you need a replacement string. The replacement string cannot contain the patterns, but it can contain back-references to the captured groups (numbered or named ones).

In Java, back-references are referenced to with $+number notation.

So, using ((?:\d+\.)?\d+)\s regex, and a $1* replacement string, you can get what you need: 1.456*substance.

See your updated regex demo.

Note that to match float values, you may consider using (\d+(?:\.\d+)?)\s or (\d*\.?\d+)\s regex patterns. For a complex pattern to match all kinds of float numbers, see Matching Floating Point Numbers with a Regular Expression at regular-expressions.info.