how to clear part of vector in time efficient way?

问题

How can I take part of the vector and fill other part with zero in time efficient way ?

I have a vector ;

 A  |  |                               A  | 0 |               
    |  |                                  | 0 |
    |  |                                  | 0 |
    |  | <-------- x         -----------> |   |  <--|
    |  |                                  |   |     |
    |  |                                  |   |     |     data in this region
    |  |                    after         |   |     |      is not changed
    |  |                                  |   |     |     
    |  |                  operation       |   |     |
    |  |                                  |   |     |
    |  |                                  |   |  <--|
    |  | <--------- y        -----------> |   |
    |  |                                  | 0 |
    |  |                                  | 0 |
    |  |                                  | 0 |

回答1:

u = 1:10;
v = [1:3, 8:10];

u(v) = 0;

Will set the first and last 3 elements to zero. To make it more similar to how you phrased the question:

x = 3;
y = 8;
u = 2:2:20;
v = x:y;
w = 1:length(u);

u(setdiff(w, v)) = 0;

Although you would probably prefer to just do:

u(1:x-1) = 0;
u(y+1:end) = 0;

(The +/-1 is only if you want inclusive range.)

回答2:

Alternatively, you can use logical indexing.

n = 20;
x = rand(n,1); %# sample content
i = 1:n; %# indices
x(~(i>3 & i<n-2)) = 0;
x

x =

         0
         0
         0
    0.2435
    0.9293
    0.3500
    0.1966
    0.2511
    0.6160
    0.4733
    0.3517
    0.8308
    0.5853
    0.5497
    0.9172
    0.2858
    0.7572
         0
         0
         0

来源：https://stackoverflow.com/questions/10733703/how-to-clear-part-of-vector-in-time-efficient-way