Re: Conditionals with multiple tests?
- To: mathgroup at smc.vnet.net
- Subject: [mg24151] Re: [mg24104] Conditionals with multiple tests?
- From: BobHanlon at aol.com
- Date: Wed, 28 Jun 2000 02:12:03 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
In a message dated 6/27/2000 1:05:15 AM, siegman at stanford.edu writes:
>Let's say I want to assign values to three variables p1, p2, p3 that
>will depend on five different (and nonoverlapping) tests test1 to test
>5.
>
>One way to do this is obviously
>
> p1 = Which[test1, value11, test2, value12, . . . ]
> p2 = Which[test1, value21, test2, value22, . . . ]
> p3 = Which[test1, value31, test2, value32, . . . ]
>
>But a more compact and (for me anyway) neater approach is
>
> Which[test1, p1=value11; p2=value21; p3=value31,
> test2, p1=value21; p2=value22; p3=value32,
> test3, . . .
> test4, . . .
> test5, . . . ]
>
>Is this form legal? That is, can one use:
>
> Which[test1, expr1, test2, expr2, . . .]
>
>where expr1, expr2, . . . may be compound expressions?
>
>(I would say that The Mathematica Book is not at all clear on this
>point, as regards either Which[] or If[].)
>
>If not, is there a legal way to implement the basic objective?
As long as a test is not encountered which gives neither True nor False, the
syntax is very flexible. These four different forms work:
Clear[p1, p2, p3];
{p1, p2, p3} = Which[True, {value11, value21, value31},
True, {value12, value22, value32} ]
{value11, value21, value31}
{p1, p2, p3} = Which[False, {value11, value21, value31},
True, {value12, value22, value32} ]
{value12, value22, value32}
Which[True, {p1, p2, p3} = {value11, value21, value31},
True, {p1, p2, p3} = {value12, value22, value32} ]
{value11, value21, value31}
Which[False, {p1, p2, p3} = {value11, value21, value31},
True, {p1, p2, p3} = {value12, value22, value32} ]
{value12, value22, value32}
Which[True, {p1 = value11, p2 = value21, p3 = value31} ,
True, {p1 = value12, p2 = value22, p3 = value32}]
{value11, value21, value31}
Which[False, {p1 = value11, p2 = value21, p3 = value31} ,
True, {p1 = value12, p2 = value22, p3 = value32}]
{value12, value22, value32}
Which[True, p1 = value11; p2 = value21; p3 = value31 ,
True, p1 = value12; p2 = value22; p3 = value32]
value31
{p1, p2, p3}
{value11, value21, value31}
Which[False, p1 = value11; p2 = value21; p3 = value31 ,
True, p1 = value12; p2 = value22; p3 = value32]
value32
{p1, p2, p3}
{value12, value22, value32}
Bob Hanlon