find all variables in a mathematical expression

Asked Jun 01 '21 at 11:30

Active Jun 01 '21 at 11:39

Viewed 107 times

I have a mathematical expression, for example : "x45 + x3/2 + ln(x1 - x45)" and I want to create a function, called

find_variables(expression)

which should return the list of the variables contained in the expression, with only one occurrence if the variable appears twice or more in the expression. Here, L = ["x45", "x3", "x1"]

I thought I might use regexes of this kind :

pattern = re.compile(x\d+)

but I don't know how to match then stock the results. Can anyone help me ?

Thank you in advance

edited Jun 01 '21 at 11:38

asked Jun 01 '21 at 11:30

BJB ChessEmperor

`set([x.replace('/', '') for x in re.findall(r'x\d+(?:/\d+)?', expression)])`? – Wiktor Stribiżew Jun 01 '21 at 11:33
`L = ["x45", "x32", "x1"]`? Should that second one be `x3`, since it's the variable being divided by two. – paxdiablo Jun 01 '21 at 11:35
[Have you looked at the documentation for the `re` package?](https://docs.python.org/3/library/re.html#re.findall) – GPhilo Jun 01 '21 at 11:36
Ok thank you, just I don't understand all the elements, mostly why should do "x.replace("/", "") – BJB ChessEmperor Jun 01 '21 at 11:37
oh yes you're right paxdiablo :) I'll just correct that – BJB ChessEmperor Jun 01 '21 at 11:37
SO I understand Stribizew's answer now xD – BJB ChessEmperor Jun 01 '21 at 11:38
1

But if you need `x3` and not `x32`, all you need is `re.findall` + `set` – Wiktor Stribiżew Jun 01 '21 at 11:38
You can use `\bx\d+\b` and return a set – The fourth bird Jun 01 '21 at 11:38
Ok, now I understand, and is this guaranteeing to me that there will be no duplication ? That's the way .findall goes ? – BJB ChessEmperor Jun 01 '21 at 11:39
The deduplication comes from the `set`, findall finds *all* occurrences, with duplicates. – GPhilo Jun 01 '21 at 11:48
ok GPhilo, that makes sense because in mathematics {1,2,5,6,9,9} = {1,2,5,6,9} for the sets thank you – BJB ChessEmperor Jun 01 '21 at 12:00

find all variables in a mathematical expression

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