# create a array base on specific condition ?

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MUKESH KUMAR on 30 Aug 2018
Commented: MUKESH KUMAR on 31 Aug 2018
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 on 30 Aug 2018
Question unclear. Please show the complete output of your example. What do you want to do with the last value?
MUKESH KUMAR on 30 Aug 2018
In the B matrix, I just want to put the difference of number at that position to the next non zero number.

Stephen Cobeldick on 30 Aug 2018
Edited: Stephen Cobeldick on 30 Aug 2018
>> 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

MUKESH KUMAR on 31 Aug 2018
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.
Stephen Cobeldick on 31 Aug 2018
@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
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 on 31 Aug 2018
sorry for that I found correction needed from my side, thanks alot.

jonas on 30 Aug 2018
v=A(find(A~=0));
vid=find(A~=0);
B=A
B(vid)=B(vid)-[v(2:end) 0]
not the most elegant solution