vectorization

Can someone give me a push in the right direction regarding vectorising a loop. Is it possible to vectorise any loop? If so, I have the following script:

Names = fieldnames(Data);
for i = 1:length(fieldnames(Data));
    for j = 1:length(Data.(Names{i}));
        index = (Data.(Names{i}){j,1}(:, 1)==211);
        Data.(Names{i}){j,1} = Data.(Names{i}){j,1}(index, :);%
    end
end

Where 'Data' is a (1x3) structure. Although this particular loop doesn't take long to run, it seems like a good place to start to learn how to vectorise instead of using loops.

Any advice would be much appreciated.

[Walter Roberson]

There are loops which cannot be vectorized. (I have not examined your code to see if yours is one of them.)

[Sean de Wolski]

I think you should describ ehow data is organized and how it's indexed. I think you might be able to simplify that which would in turn make vectorization easier.

[Richard]

The structure 'Data' has 3 fields, called 'data1', 'data2', and 'data3' which are expressed by 'Names'. The index then goes through the first column in each matrix in 'Data.(Names)' to produce a matrix where only the rows which begin with 211 are kept.

I hope this is clearer.

Answer 1

[Jan]

A simplification - please test if this is faster already, although it is not vectorized:

Names = fieldnames(Data);
for i = 1:length(fieldnames(Data));
  Names_i = Data.(Names{i});
  for j = 1:length(Names_i);
    index = Names_i{j,1}(:, 1)==211;
    Names_i{j,1} = Names_i{j,1}(index, :);
  end
  Data.(Names{i}) = Names_i;
end

If the cells stored in the field are {N x 1} cell vectors, omitting the second index saves time: Names_i{j} instead of Names_i{j,1}.