Question

I have a 4-dimensional dictionary I made with a Python script for a data mining project I’m working on, and I want to read the data into Matlab to do some statistical tests on the data.

To read a 2-dimensional matrix is trivial. I figured that since my first dimension is only 4-deep, I could just write each slice of it out to a separate file (4 files total) with each file having many 2-dimensional slices, looking something like this:

2 3 6
4 5 8

6 7 3
1 4 3

6 6 7
8 9 0

This however does not work, and matlab reads it as a single continuous 6 x 3 matrix. I even took a look a dlmread but could not figure out how to get it do what I wanted. How do I format this so I can put 3 (or preferably more) dimensions in a single file?

Answer 1

A simple solution is to create a file with two lines only: the first line contains the target array size, the second line contains all your data. Then, all you need to do is reshape the data.

Say your file is

3 2 3
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

You do the following to read the array into the variable data

fid = fopen('myFile'); %# open the file (don't forget the extension)
arraySize = str2num(fgetl(fid)); %# read the first line, convert to numbers
data = str2num(fgetl(fid)); %# read the second line
data = reshape(data,arraySize); %# reshape the data
fclose(fid); %# close the file

Have a look at data to see how Matlab orders elements in multidimensional arrays.