How to delete/subtract/make zero all the values above a specific value?

My data has three columns. I want to do three things. 1) In the first analysis, I want to delete all the values above 255.

2)In the second analysis I want to make all the values above 255 to zero.

3)In the third analysis, I want just to take all the values above 255 and subtract 255 from it.

How can I do these. Please note that these all are not in a single analysis. These are three different analysis of a data.

I have tried the following:

 index1 = find(Data(:,1)>=256&Data(:,2)<=256&Data(:,3)<=256);
 Data(index1,:)=[]; %I think this can delete all above 255. But if I want to subtract by 255 and to replace with zeros, what should I do?

I am confused how to do in the second line! I know if I need to remove, I just need to replace Data-256 by []. But to make it zero and to subtract by 255, what should I do?

Answer 1

[Sajjad Yazdani]

For the first one use:

Data(Data(1,:)>255,:)=[];

For the second analysis :

Data(Data>255)=0;

And for last analysis :

Data(Data>255)=Data(Data>255)-255;

Remind that Logic indexing is more better than find() and more faster.

Answer 2

[Andrei Bobrov]

t = D > 255;

out1 = D(~t);

out2 = D;
out2(t) = 0;

out3 = D;
out3(t) = out3(t) - 255;