use of eval

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?

Answer 1

[Wayne King]

Your call to input() returns the string bar in whatplot

but whatplot(plots) is not a string.

    eval([whatplot '(plots)'])

[Tor Fredrik Hove]

I cant seem to get this right:

plots=[3 4 6 1]

plots =

3 4 6 1

>> whatplot='bar'

whatplot =

bar

>> eval([whatplot'(plots)'])

??? eval([whatplot'(plots)'])

|

Error: Unbalanced or unexpected parenthesis or bracket.

>>

[Andrei Bobrov]

eval([whatplot, '(plots)'])

[Tor Fredrik Hove]

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]

Bad book. Evil EVAL.

Answer 2

[Patrick Kalita]

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 )

[Fangjun Jiang]

Yes. feval() is the way to go. I was thinking about inline(), @, etc.

[Jan]

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

[Tor Fredrik Hove]

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

Answer 3

[Wayne King]

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

[Wayne King]

also, see the comments by other posters above.