create a array base on specific condition ?

I had a array like this

A=[0 0 0 10 0 0 0 0 8 0 0 5 0 0 0 3 0 2 0 0 0 1 0 0 0];

and now I want to create a array B like this in which

B(4)=10-8=2;
[B(4)=A(4)-next upcoming non zero value ],
B(9)=8-5=3;[B(9)=A(9)-next non zero value]

and similarly for

B(12)=5-3=2;
B(16)=3-2=1;
B(18)=2-1=1;
B(22)=1;

and rest of the B values are zero. thanks

[jonas]

Question unclear. Please show the complete output of your example. What do you want to do with the last value?

[MUKESH KUMAR]

In the B matrix, I just want to put the difference of number at that position to the next non zero number.

Answer 1

[Stephen23]

>> idx = A~=0;
>> A(idx) = [-diff(A(idx)),1]
A =
   0   0   0   2   0   0   0   0   3   0   0   2   0   0   0   1   0   1   0   0   0   1   0   0   0

[jonas]

+1 always quick with the efficient solution :)

[Stephen23]

@jonas: thank you.

[MUKESH KUMAR]

But in my case, I got -ve values when applied code to my problem.In B, first data is incorrect according to this but rest are negatives.

[Stephen23]

@MUKESH KUMAR: you get negative values because although in your question you gave values which decrease in magnitude (so their differences are all positive), in your real A data all of the values increase in magnitude (so their differences are all negative). Lets have a look at some of the values:

>> B(find(B))
ans =
  -1
  -5
  -3
  -2
 ... lots more here
  -3
  -2
   1
>> A(find(A))
ans =
     1
     2
     7
    10
    12
    13
  ... lots more here
   128
   131
   133

In your question you wrote: "I had a array like this"

A=[0 0 0 10 0 0 0 0 8 0 0 5 0 0 0 3 0 2 0 0 0 1 0 0 0];

"and now I want to create a array B like this in which"

B(4)=10-8=2;
[B(4)=A(4)-next upcoming non zero value ],
B(9)=8-5=3;[B(9)=A(9)-next non zero value]

Lets try your exact calculation method with the real A values:

B(6334) = A(6334) - A(6478) = -1
B(6478) = A(6478) - A(7487) = -5
B(7487) = A(7487) - A(7543) = -3
...etc

All are negative, all follow the method that you gave in your question, and all are exactly the values that are in B.

[MUKESH KUMAR]

sorry for that I found correction needed from my side, thanks alot.

Answer 2

[jonas]

v=A(find(A~=0));
vid=find(A~=0);
B=A
B(vid)=B(vid)-[v(2:end) 0]

not the most elegant solution