5
votes
2answers
253 views

DownValue “associative array” to list? [duplicate]

I have a "sparse array" like this arr[1.5]=0.4, arr[3.5]=0.7, arr[7]=0.3 which is not really a sparse array since the keys are not all integers. This is like a ...
8
votes
2answers
380 views

How to get the list of defined values for an indexed variable?

I would like a table with rational indexes - thus it would be practical to use a dictionary, which, in Mathematica are implemented with the indexed variables. I would like to be able to do: ...