How to Get one Property of a Structure Array Using a Property on the Same Line

Hello all,

I'm a novice at MatLab (I'm taking a course on it), but I want to use it to be able to access atomic masses without needing to look at the back of my back for a course. I found a CSV of the atomic masses of every isotope, and I've made it into a structure array using a for loop. Basic stuff.

rawMassData = readcell('IUPAC-atomic-masses.csv');
for i=3:length(rawMassData)
    isotopicMasses(i).name = rawMassData{i,1};
    isotopicMasses(i).mass = rawMassData{i,2};
    isotopicMasses(i).uncertainty = rawMassData{i,3};
end

The question I have is how do I now get the mass of a certain isotope? One field in the structure array is all the names, so I should just be able to index into the structure by name, find the line that that isotope is on, and get the mass on that same line right? I just don't know how to do that.

[Voss]

It's better to use size rather than length.

for i=3:size(rawMassData,1)

Answer 1

[Voss]

name = 'deuterium'; % name of the isotope you want the mass of

idx = strcmp({isotopicMasses.name},name);
mass = isotopicMasses(idx).mass;

[Tom]

Thank you! This was exactly what I was looking for.

[Voss]

You're welcome! Any questions, let me know.

Answer 2

[Steven Lord]

You could do what you described by making a non-scalar struct, each element of which has three fields, each of which has a piece of text or a number. Another approach would be to create a scalar struct, each field of which is named for an element, and which contains a struct.

elements.carbon = struct('number', 6, 'mass', 12.011)

elements = struct with fields:
    carbon: [1x1 struct]

elements.carbon

ans = struct with fields:
    number: 6
      mass: 12.0110

Since you're reading the data from a file, you'd need to use dynamic field names to create the field.

name = 'oxygen';
elements.(name) = struct('number', 8, 'mass', 15.999)

elements = struct with fields:
    carbon: [1x1 struct]
    oxygen: [1x1 struct]

Alternately, since your data is tabular in nature, consider creating it as a table array rather than a struct.

names = ["carbon"; "oxygen"];
number = [6; 8];
mass = [12.011; 15.999];
elementsT = table(number, mass, RowNames = names)

elementsT = 2x2 table
              number     mass 
              ______    ______

    carbon      6       12.011
    oxygen      8       15.999

To retrieve the data, you can use curly braces or dot notation.

elementsT{'carbon', 'mass'}

ans = 12.0110

allMasses = elementsT.mass

allMasses = 2x1

12.0110 15.9990

<mw-icon class=""></mw-icon>

<mw-icon class=""></mw-icon>