# Using list of rules from imported .mat file

I'm attempting to learn Mathematica to replace MATLAB. However, I have some data in .mat files which contains named variables.

Whenever I import the .mat file, I get a list of rules. What's the best way to go about using these? Let's say I wanted to plot some of the LabeledData, say "n2_den". Would I do something like ListLinePlot[data]/.n2_den? Or would I be better off just converting the list of rules to a list like one of the recommendations shows when I import?

• Turn it into an Association. That's the equivalent to the structure arrays (struct) in Matlab. Btw., see here for more hints on how to transplate between Matlab and Mathematica. Jan 14, 2019 at 22:33
• I really like this suggestion Henrick! I makes a lot of sense in how to now use the data I've imported. Jan 16, 2019 at 18:55
• I am glad that this helped you. Welcome on Mathematica.StackExchange and have fun with Mahematica! Jan 16, 2019 at 21:15

For your case (in a verbose style to clarify structure):

mydata = {earth_alts -> {{3}, {4}, {5}}};

myEarthAltsData = mydata[[1, 2]]


Here, mydata[[1,2]] takes the second part of the (first) association, i.e., gives just the list of values.

• That works great, thanks! Just as a follow-up then, what does it mean doing mydata[[1,2]] in terms of rules? I get the indexing in thinking about multidimensional lists, but not rules necessarily. Jan 15, 2019 at 0:07
• @Bo, the this axiom of Mathematica is: "Everything is an expression.". And expressions are basically trees into which you can index with Part ([[...]]). In case of mydata[[1,2]] have a look at the internal representations by executing TreeForm[mydata] and TreeForm[mydata[[1, 2]]]. Do you see the pattern? Jan 16, 2019 at 21:20
• That's a really neat way to visualize what's happening here, thanks for pointing it out @HenrikSchumacher! Jan 16, 2019 at 22:42

Turn it into an Association. That's the equivalent to the structure arrays (struct) in Matlab.

Btw., see here for more hints on how to translate between Matlab and Mathematica.