Product of non-zero elements in sparse array

Question

How can I multiply the non-zero elements of a SparseArray?

Example:

a = SparseArray[{1 -> 1, 3 -> 2, 7 -> 3}]
Times @@ a (* this returns 0, but I need 6! *)

Related: http://mathematica.stackexchange.com/a/31963/121 – Mr.Wizard Feb 06 '14 at 14:14 — Mr.Wizard, Feb 06 '14 at 14:14

score 6 · Accepted Answer · answered Feb 06 '14 at 13:37

6

Please note the following:

The sparse array a is:
```
 {1, 0, 2, 0, 0, 0, 3}
```
hence applying Times to this yields zero
You can see the underlying array using Normal
```
  a // Normal
```
You could multiply the non-zero elements of a sparse array object:
```
 Times @@ a["NonzeroValues"]
```

answered Feb 06 '14 at 13:37

ubpdqn

This is good to know! Could you perhaps point me to the documentation where "NonzeroValues" is mentioned? – Danvil Feb 06 '14 at 13:42
2

@Danvil As far as I know it isn't documented. You can see the other SparseArray Properties with: SparseArray[{1}]["Properties"]. I gathered links to some of my uses of these in this answer. – Mr.Wizard Feb 06 '14 at 14:12

1 Answers1