Forum Discussion
Access Analytic Power Query challenge: Ticket list
re: Side note.
I, too, user recursion very rarely. I believe the time it comes into its own is when one has a termination criterion but little knowledge of how many steps will be required to satisfy the condition. Examples might include minimising a non-linear objective function or integrating ordinary differential equations using a variable step length method. Things I might try one day, but have yet to tackle. I think lori_m may have a more informed opinion as well as some examples.
Yes, as per Peter's comment, one can distinguish two types of lambda definition:
Standard (non-recursive): function applied a given number of times
e.g. data transformations (e.g. this one), multi-dimensional arrays, linear optimisation
Recursive: function applied repeatedly until a condition is met
e.g. search problems, numerical solvers, non-linear optimisation, even machine learning
While many of the recursive examples might be considered a stretch to accomplish using formulas alone, it only takes for a lambda to be made available by someone in order for anyone else to apply it (e.g. Sudoku attachment). A good learning exercise for me was to write a recursive lambda to find the IRR of a list of values using either bisection or Newton-Raphson methods, and then check against the built-in function.
- That is a pretty amazing formula. Even the formula to calculate the possible values for a given cell is elegant. I separated that formula out and the concatenated the values to help a manual solution.
I still find recursive formula intensely difficult to set up and test and this one has the two recursive loops to contend with!I didn't come up with the method of solution. The formula is a pretty direct translation of the linked python code originally from R. I also wondered about applying similar logic to chess puzzles: eight queens, knight's tour, even a simple chess playing program. Hoping someone will rise to the challenge!