Forum Discussion
Recursive functions in dataflows
Hi,
Has anyone tried writing recursive functions in dataflows. I was just moving a dataset into a dataflow and what works fine as a dataset complains about cyclic reference being created.
Recursive functions are quite handy when dealing with hierarchical data structures so would be a shame if they don't work in data flows.
I Struggled with this for a while as well. It seems the solution is as simple as using an @ sign.
This is an example my coworker wrote.
let f = (n as number) as number => if n = 0 then 0 else if n = 1 then 1 else @f(n - 2) + @f(n - 1) in f
I've tested it and it works in dataflows. Note, when you make the recusive call, be sure to reference the name of the function from inside the let. For example, say the external name for this is 'fib', you need to make the recursive call with @f(..). I hope this helps!
Edit:
This is addressed on page 28 of the reference manual.
https://docs.microsoft.com/en-us/powerquery-m/power-query-m-language-specification
5 Replies
Are you doing this in M? This is a functional language and the issue may be related to tail code optimization that most functional languages do. I don't know whether the M compiler does that, but more than likely the answer is somewhere in how this works. Perhaps you can use functions and external code exposed to do some of this. We have had to do that in some of our use cases.
Good luck.
I Struggled with this for a while as well. It seems the solution is as simple as using an @ sign.
This is an example my coworker wrote.
let f = (n as number) as number => if n = 0 then 0 else if n = 1 then 1 else @f(n - 2) + @f(n - 1) in f
I've tested it and it works in dataflows. Note, when you make the recusive call, be sure to reference the name of the function from inside the let. For example, say the external name for this is 'fib', you need to make the recursive call with @f(..). I hope this helps!
Edit:
This is addressed on page 28 of the reference manual.
https://docs.microsoft.com/en-us/powerquery-m/power-query-m-language-specification