use of eval

Question

Tor Fredrik Hove 2011-10-21

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采纳的回答： Wayne King

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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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Answer 1

Wayne King 2011-10-21

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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 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 2011-10-22

Bad book. Evil EVAL.

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Answer 2

Patrick Kalita 2011-10-21

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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 2011-10-21

@Tor: Avoid EVAL. As you see, it causes troubles.

Tor Fredrik Hove 2011-10-21

it is part of curriculum unfortunately:) If not I would have:)

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Answer 3

Wayne King 2011-10-21

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plots=[3 4 6 1];
whatplot = 'bar';
eval([whatplot '(plots)'])

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Wayne King 2011-10-21

also, see the comments by other posters above.

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