use of eval

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Tor Fredrik Hove
Tor Fredrik Hove 2011-10-21
I am trying to use evalfunction but are having a hard time:
>> plots=[3 4 6 1]
plots =
3 4 6 1
>> whatplot=input('type type of graph: ','s')
type type of graph: bar
whatplot =
bar
>> eval(whatplot(plots))
??? Index exceeds matrix dimensions.
>>
why wont it evaluate it to a graph with bars?

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Wayne King
Wayne King 2011-10-21
Your call to input() returns the string bar in whatplot
but whatplot(plots) is not a string.
eval([whatplot '(plots)'])
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Tor Fredrik Hove
Tor Fredrik Hove 2011-10-21
thanks! I guess I am also a bit confussed about my book. It says:
>>x=[9 7 10 9];
whatplot=input('What type of plot?: ','s');
What type of plot?: bar
>>eval([whatplot '(x)'])
>>title(whatplot)
>>xlabel('Student#')
>>ylabel('Quiz Grade')
I guess the three last lines are just for naming graph and coordinates but thoose before don't return any graph for me
Jan
Jan 2011-10-22
Bad book. Evil EVAL.

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Patrick Kalita
Patrick Kalita 2011-10-21
I think feval would be a better option here. It is a safer than eval, and it easily accommodates passing input arguments:
feval( whatplot, plots )
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Jan
Jan 2011-10-21
@Tor: Avoid EVAL. As you see, it causes troubles.
Tor Fredrik Hove
Tor Fredrik Hove 2011-10-21
it is part of curriculum unfortunately:) If not I would have:)

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Wayne King
Wayne King 2011-10-21
plots=[3 4 6 1];
whatplot = 'bar';
eval([whatplot '(plots)'])
  1 个评论
Wayne King
Wayne King 2011-10-21
also, see the comments by other posters above.

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