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From: S. B. Gray on 8 Jul 2010 03:13
I have lists such as

th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501,
462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}

and I want to find the position of the last nonzero element (e.g. 3 at
position 25). Trivial, but some poking around did not reveal a neat way.

Anyone? Thank you.

Steve Gray

From: Fred Simons on 8 Jul 2010 06:50
Op 08-07-2010 09:13, S. B. Gray schreef:
> I have lists such as
>
> th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501,
> 462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0,
> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
>
> and I want to find the position of the last nonzero element (e.g. 3 at
> position 25). Trivial, but some poking around did not reveal a neat way.
>
> Anyone? Thank you.
>
> Steve Gray
>
>
>
Length[th] - LengthWhile[Reverse[th], # == 0 &]

Regards,

Fred Simons
Eindhoven University of Technology

From: David Park on 8 Jul 2010 06:50
Position[th, Except[0], {1}] // Last

{25}


David Park
djmpark(a)comcast.net
http://home.comcast.net/~djmpark/


From: S. B. Gray [mailto:stevebg(a)ROADRUNNER.COM]

I have lists such as

th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501,
462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}

and I want to find the position of the last nonzero element (e.g. 3 at
position 25). Trivial, but some poking around did not reveal a neat way.

Anyone? Thank you.

Steve Gray



From: Bob Hanlon on 8 Jul 2010 07:41

th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501,
462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};

th /. {a___, 0 ..} :> {a} // Length

25

th /. {a___, 0 ..} :> Length[{a}]

25


Bob Hanlon

---- "S. B. Gray" <stevebg(a)ROADRUNNER.COM> wrote:

=============
I have lists such as

th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501,
462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}

and I want to find the position of the last nonzero element (e.g. 3 at
position 25). Trivial, but some poking around did not reveal a neat way.

Anyone? Thank you.

Steve Gray



From: Carl K. Woll on 8 Jul 2010 20:35
On 7/8/2010 2:13 AM, S. B. Gray wrote:
> I have lists such as
>
> th = {227, 342, 527, 0, 670, 730, 703, 0, 0, 649, 687, 614, 570, 501,
> 462, 402, 325, 254, 189, 99, 81, 36, 9, 8, 3, 0, 0, 0, 0, 0, 0, 0,
> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
> 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
>
> and I want to find the position of the last nonzero element (e.g. 3 at
> position 25). Trivial, but some poking around did not reveal a neat way.
>
> Anyone? Thank you.
>
> Steve Gray
>
>

One can use SparseArray to do this:

In[46]:= SparseArray[th] /. SparseArray[_, _, _, {_, {_, pos_}, _}] :>
pos[[-1, 1]]

Out[46]= 25

Carl Woll
Wolfram Research

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