What am I missing while using cellfun & eval together

Question

Daniel 2020-1-8

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评论： Daniel 2020-1-9

sc = statechart1;
Prop = {'Config','DBIT'}
y = table('Size', [l 2], 'VariableTypes',{'double','logical'},'VariableNames', Prop);
for i=1:l
    step(sc);
    cellfun(@(x) eval("y." + x + "(i) = sc." + x + ";"),Prop);
end

The preceeding code produces the following error:

Unable to resolve the name sc.ConfigDuration

Now it is possible to fix by replacing the cellfun with:

for k=1:length(Prop)
    eval("y." + Prop{k} + "(i) = sc." + Prop{k} + ";");
end

But for my own learning it would be nice to know what I'm missing with the cellfun implementation.

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Answer 1

Steven Lord 2020-1-8

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There's no need to use eval here. Instead, I would use table array indexing on y. I believe dynamic property indexing will work on statechart1, which I assume is a standalone chart, but I'm not 100% certain. Something along the lines of this should work, though I haven't tested it. I changed the variable names i (to whichstep) and lower-case L (to numberOfSteps) you used in your code for readability and to make them more clearly indicate their purposes.

sc = statechart1;
Prop = {'Config','DBIT'}
y = table('Size', [numberOfSteps 2], 'VariableTypes',{'double','logical'},'VariableNames', Prop);
for whichstep = 1:numberOfSteps
    step(sc);
    for whichprop = Prop
        name = whichprop{1};
        y{whichstep, name} = sc.(name);
    end
end

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Daniel 2020-1-9

Thanks Steven,

Although your code didn't work directly, not that you promised. Dynamic field referencing seems to have passed me by, allowing me to remove most of the eval() calls in my code saving a lot of runtime.

So the above chuck of the code I was able to reduce to

sc = statechart1;
Prop = {'Config','DBIT'};
y = table('Size', [numberOfSteps 2], 'VariableTypes', {'double','logical'},'VariableNames', Prop);
for whichstep = 1:numberOfSteps
    step(sc);
    y(whichstep, Prop) = cellfun(@(x), Prop,'UniformOutput',false);
end