choose B or C or D if A does not exist - how to write this?

Hi all,

I have the following:

switch joint        
    case 'Knee'
        prox = 'HipJC';
        dist = 'LEPI';
        wand = 'THPA' ;       
    end

side = {'R','L'};
for i = 1:length(side)
    wandMk = data.([side{i},wand]).line;
end

I got the following error: Unrecognized field name "LTHPA", which is because 'LTHPA' does not exist in my structure.

I could use 'THPP' or 'THDA' or 'THDP' instead of 'THPA', because I know these exist. Hence, how could I rewrite the above for this to run?

For example:

if 'THPA' does not exist then

wand = 'THDA' or 'THDA' or 'THDP'

Thanks!

[Stephen23]

Use https://www.mathworks.com/help/matlab/ref/isfield.html

Answer 1

[Paul]

Create an example structure

data.THDA = 1;data.THPP = 2;data.THDP = 3;

Use fieldnames to get the fields of data

fnames = fieldnames(data)

fnames = 3x1 cell array
    {'THDA'}
    {'THPP'}
    {'THDP'}

Field to test

wand = "LTHPA"

wand = "LTHPA"

Reassign if invalid field

if ~any(strcmp(wand,fnames))
    wand = "THDA"
end

wand = "THDA"

data.(wand)

ans = 1

[Paul]

Use isfield instead of strcmp/fieldnames Thanks @Stephen23! How did I not know about that function (rhetorical question)?