matlab - How iterate with a certain value? -

i newbie in matlab. want find way in python iterate on values.

in python that:

for in [0, 90, 180, 360]:     print('degree', i) 

but, how in matlab?

short version:

do this:

myvar = [0, 90, 180, 360]; = 1:size(myvar, 2)     ival = myvar(:, i);     disp(['degree', num2str(ival)]); end 

long version:

matlab doesn't have equivalent python iterators. loop rules fundamentally different.

your code work matlab written in python:

for = [0, 90, 180, 360]     disp(['degree', num2str(i)]); end 

however, because special case in matlab that, coincidence, happens have similar result 1 in python. matlab doing different, seemingly similar code work in python silently different thing in matlab.

python's loop rules depend on iterator protocol, iterable classes lists , numpy arrays follow. generally, loops on "outer" sequence. in nested lists, outermost list. in numpy arrays, last dimension.

matlab's loop rules follow: flattens matrix 2d matrix if has more 2 dimension, loops on second dimension. in other words, nth time through loop gives nth column of loop variable, after loop variable has been flattened 2d matrix. in case, have 2d matrix first dimension 1 , second dimension 4. loops on second dimension, giving 4 1x1 matrices (there no such thing 1d or 0d data types in matlab there in python).

however, if had column vector, this:

for = [0; 90; 180; 360]     disp(['degree', num2str(i)]); end 

you error:

error using horzcat dimensions of matrices being concatenated not consistent 

... because instead of getting 4 1x1 matrices 1 4x1 matrix, because original matrix 4x1 matrix , has second dimension of 1. if start 4x5 matrix, 5 4x1 matrices. if start 4x5x6 matrices, 30 (5*6) 4x1 matrices.

also, returns same data type got in. if start 1x4 cell array, 1x1 cell arrays out, rather whatever in cell array. there isn't point using cell arrays directly, either.

overall, means using variable directly in loop, this:

for = myvar    % end 

...is extremely dangerous in matlab. works reliably if can absolutely 100% sure myvar row vector. if try expand code, or use in new situation, can silently wrong thing. , other matlab internal features , functions silently wrong thing, easy sort of code seem work fine giving wrong result.

so see sort of approach in matlab, people use index variable. create sequence of indices in loop , loop on those. common approach this

myvar = [0, 90, 180, 360]; = 1:length(myvar)     ivar = myvar(i); end 

so in case i index of myvar want use. approach, although common, dangerous. unlike numpy len gives consistent dimension (the first one), length in matlab gives longest dimension, whatever might be. acts unpredictably if given 2d matrices. , because matlab treats single indices indices of flattened version of matrix, again silently wrong thing.

so safe way of doing manually specify dimension want using size function, or if want loop on values in multidimensional array use numel function total number of elements:

for i=1:size(myvar, 2)    ivar = myvar(:, i); end  i=1:numel(myvar)    ivar = myvar(i); end