MATLAB: Import CSV files, find extraction condition, and local maxima

csv

Hi everyone,

I am trying to read in multiple .csv files with lot of data (mostly numbers except : the first row contains 2 strings and several numbers, and these first row numbers are actully the same in every .csv)

After that I have to find in the first row the value '50' and get its column and then find the local maxima in that.

Can you pls help me, how to solve this?

Thanks in advance.

Best Answer

Grace:

This should do it:

% Create sample matrix.
m = randi(500, 100, 30);
% Find out all the rows that have a 50 in them.
rowsWith50 = find(any(m == 50, 2))
% If any row(s) do, then find the column with the 50 in it, 
% and get the max of that column.
if ~isempty(rowsWith50)
	firstRowWith50 = m(rowsWith50(1), :);
	% Get its column
	columnWith50 = find(firstRowWith50 == 50, 1, 'first')
	% Find the max of this column over all rows
	theMax = max(m(:, columnWith50))
end

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MATLAB: File-loop, for loop,importing excel data

%Read each CSV file, change the text data to numeric and work with it
clear;
clc;
dirroot='C:\Documents\Excel\';
for L=1:2
    
    dirname     = [dirroot, 'L', num2str(L)];
    files       = dir([dirname,'*.csv']);             % Listing all files in the given 
                                                            % directory with the extension of csv
    filenames   = {files.name};
    
    for i=1:size(filenames, 2)                              % load all the csv files separately
                                                  
        t           = readtable(string(filenames{i}));      % Give me the csv file in a table
        t.Var1      = str2double(string(t.Var1));           % convert the first 2 variables from characters in cells to doubles
        t.Var2      = str2double(string(t.Var2));           % text is replaced by NaN (not a number)
        data        = table2array (t);                      % convert to double array
        
        [rows, columns] = size(data);                       % The size of the matrix (the number of
                                                            % elements is the same for all columns
                                                            % in a matrix, also nr 16)
        is_max_rows      = islocalmax(data(:,16))           % logical vector of all local max in
                                                            % column 16
        local_max_col_16 = data(is_max_rows, 16)            % value of local maxima in column 16
        
        [rowsWith50, colsWith50] = find(data == 50);        % Find out all the rows/cols that have a 50
                                                            % in them.
        theMax = max(data(:,unique(colsWith50)))            % get the max of the columns with  a 50
                                                            %  without repetition of the columns with
                                                            % 2x or more 50
                                                            
        save([dirname, 'results_L_', num2str(L), '_dataset_', num2str(i)]); % save data
    end
end

It might not be the most elegant way how I did it, either. But it should work if the structure of all the files is the same (text in first 2 columns).

But lmk how you get along!

MATLAB: How to import first two columns using csvread over a specific range without knowing the total number of rows

Just read the whole thing and extract the first 2 columns

M = csvread('03.csv'); % Read entire file.
first2Columns = M(:,1:2); % Extract out the first two columns.

Best Answer

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