Variable

Hello, If i have

X=rand(20,1)
Y=rand(20,1)

then i want to do 

p1=[x(1)   y(1)]
p2=[x(2)   y(2)]
.    .      .
.    .      .
.    .      .
p20=[x(20) y(20)]

How can i intialize these p1 to p20 values with the help of loop instead of intiallizing manually?

The varaible needs to be updates as p1...p20.

Finally with structure P has terms p1...p20, with p1...p20 have their values from X and Y

Thanks in advance

Answer 1

[Andrei Bobrov]

variant use cell array

X=rand(20,1)
Y=rand(20,1)
p = mat2cell([X Y],ones(20,1),2)

bad version

for j1 = 1:size(X,1)
   jc = num2str(j1);
   eval(['p' jc '= [X(' jc '), Y(' jc ')]']);
end

So do not ever! Use the better 'p{1}' of the first variant instead of 'p1'

[developer]

but i putting them in a cell i also want to name them as p1 ...p20 so that i can address them through their variable names p1, p2 etc

[Fangjun Jiang]

See 'How can I create variables A1, A2,...,A10 in a loop?' from http://matlab.wikia.com/wiki/FAQ

[Fangjun Jiang]

@andrei, why mat2cell? why can't p=[X Y]?

[Oleg Komarov]

Don't name variables sequentially as p1 to p20. Imagine the pain having to reference everytime 20 variables.

[developer]

@Komarov

But what if i put them all p1... p20 values within a structure or a cell?

[Andrei Bobrov]

Hi Fangjun, I agree with you, but I, I thought that p {1} is more similar to p1, than p (1,:) on p1 :)

[developer]

@andrei

your solution is acceptable but as Komarov mentioned , if i want to put all of them in a structure like P that has p1...p20 with values of p1...p20, then i have to define all the fields one by one?

[Fangjun Jiang]

%%

X=rand(20,1);

Y=rand(20,1);

p = mat2cell([X Y],ones(20,1),2);

f=cellstr(strcat('p',num2str((1:20)','%d')));

temp=[f p]';

P=struct(temp{:})

[Andrei Bobrov]

f=cellstr(strcat('p',strjust(num2str((1:20)'),'left')));

[Jan]

@Fangjun: Instead of creating the large intermediate array [f, p]', this is more efficient: P = cell2struct(p(:), f(:)). This is slightly faster than specifying the dimension as 3rd input of CELL2STRUCT, btw.

[Oleg Komarov]

@developer: structs and cells are fine.

[Fangjun Jiang]

Good one, Jan! My mind was stuck with the struct().