Formatting data from a csv file in MATLAB

Question

I have a large csv-file, which looks similar to the following:

My problem is related to a question previously posted and superbly answered by @gnovice. I am using the folling code to format the data.

data = csvread('datacsv.csv',1,0);
[rowVals, ~, rowIndex] = unique(data(:, 3));
[colVals, ~, colIndex] = unique(data(:, 1).');
A = accumarray([rowIndex colIndex], data(:, 2), [], @(x) x(1));  % Keeps the first value
A = [NaN colVals; rowVals A];

The output, however looks like:

It should ideally look like:

Whatis the part of the code that I have to adjust?

gnovice · Accepted Answer · 2017-11-09 21:54:32Z

1

Your date appears in the second column for this data, whereas it appeared in the third column on the previous question. Just change the index in the second line to a 2:

[rowVals, ~, rowIndex] = unique(data(:, 2));

And change the index for the accumulated data to a 3:

A = accumarray([rowIndex colIndex], data(:, 3), [], @(x) x(1));

answered Nov 9, 2017 at 21:54

gnovice

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3 Comments

Joe Over a year ago

The solution for this setting works perfectly well. Although not directly related to this question, could you please explain, why I obtain an error "Error using dlmread" - "Empty format string is not supported at the end of a file."? The real data are far larger, yet the csv-file looks the same as in the example above?

gnovice Over a year ago

@Joe: Not sure. I couldn't find a way to recreate it. I'd check the last line of your file for extra whitespace.

Joe Over a year ago

Saving the large csv-file (1.875.150 KB), the data seem to get lost as the file then has 0 KB. I fixed it and your code performs very quick!

Sylvain Lacaze · Accepted Answer · 2017-11-09 22:06:52Z

1

Another way would be to use "unstack":

myTable = readtable( 'data.csv' );
newTable = unstack( myTable, 'C', 'A' )

newTable =

  3×3 table

        B          x1         x2   
    _________    _______    _______

    2.015e+07        NaN       -2.5
    2.016e+07    -2.5625       -2.5
    2.017e+07        2.5    -2.5625

answered Nov 9, 2017 at 22:06

Sylvain Lacaze

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