MATLAB: How to extract certain columns in a vector and store it as a new vector

air pollutionarraycolumncolumn vectorextracting dataindexingmatrixozonevector

I have a a 365×30 vector called OzoneData that contains ozone pollution data per day in a year (365) and from 30 different sites. I want to take all the ozone concentrations from columns 1,27,28,15, and 13 (sites) and store them in a different vector called Group1. How can I do this?

Thank you!

Best Answer

Group1 = OzoneData(:,[1,27,28,15,13]);

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MATLAB: Vector inside a vector

A qualified no. You cannot assign anything but a scalar element to a simple array in MATLAB.

Or a qualified yes, IF the array or matrix you will store it in is a cell array, then yes, you can do as you wish. Note that working with cell arrays is not quite so simple though, as you cannot do arithmetic on those elements until you extract them form the cells that hold them. You can also use tools like cellfun.

You can also assign anything you wish to fields of a structure, so that may be an alternative to use.

MATLAB: Vectorization

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}.

Best Answer

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MATLAB: Vector inside a vector

MATLAB: Vectorization

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