How do I extract data from MATLAB figures? (2024)

When you plot a matrix by columns, then the order of handles returned from the plot() call is the order of the columns:

Now h(1) corresponds to column 1, h(2) corresponds to column 2, and so on. You can confirm this with:

and see that indeed the item labeled col5 is the one with highest average Y (it was constructed that way by the sort() call).

However, the order of axes children defaults to the reverse of this:

because the rule is that the axes children are (by default) painted from last to first (first is on top, last is on bottom). This can be altered in a few ways, including some obscure specialized settings that were new in R2014b, but also the order can be changed with good old uistack()

When you recall a figure file and pull out the axes children, the axes children are going to be in the same order as was present in the axes when it was saved to the figure file. If nothing in the original code altered the order, that is going to be last column first. So if you retrieve the YData and mat2cell() it into a 2D matrix, make sure to fliplr() to get the original order.

At this point,

• all_titles is a cell array of character vectors containing the title for each axes (in latex form)
• all_XData is a cell array with one entry for each axes, and the entry is a cell array of numeric row vectors, one entry for each line in the axes
• all_YData is a cell array with one entry for each axes, and the entry is a cell array of numeric row vectors, one entry for each line in the axes

WIth that figure, there are three lines in almost all of the axes, but one of them has four lines (the legend which is attached to one of the axes only has three names defined.)

This code permits you to select a .fig file, and processes it. It outputs a cell array of character vectors named all_titles . It outputs a cell array named all_XData in which there is one celll array entry for each axes, that contains an entry for each line inside the axes, that is the line x coordinates. It outputs a cell array named all_YData in which there is one celll array entry for each axes, that contains an entry for each line inside the axes, that is the line y coordinates. The coordinate entries have been filtered to remove any lines with Y coordinate [0 0]

The difference between this code and the previous version is that this version filters out lines where the y coordinate is just [0 0]. This version also accounts for the possibility that an axes only has one line.

In the case where the axes had more than one line, the internal get() call would have returned a cell array of coordinates, but in the case where the axes had exactly one line, the internal get() call would have returned the numeric coordinates directly: this code detects the single-line case and deliberately wraps it inside a cell array, so that the outputs are consistent.

So, for axes #K,all_titles{K} is a character vector that is the axes title, and all_XData{K} is a cell array with one entry per line inside the axes for the X coordinates, and all_YData{K} is a cell array with one entry per line inside the axes for the Y coordinates.

This code does not assume that all of the lines inside an axes have the same number of points. If you are willing to assume that, then you can process the arrays further by

and then those would be cell arrays with one entry per axes, and the entries would be N x L numeric arrays where N is the number of lines and L is the number of points in the line.