Re: How do I test for existence of a list element? Clarified

*To*: mathgroup at smc.vnet.net*Subject*: [mg112688] Re: How do I test for existence of a list element? Clarified*From*: "Sjoerd C. de Vries" <sjoerd.c.devries at gmail.com>*Date*: Mon, 27 Sep 2010 05:45:57 -0400 (EDT)*References*: <i7mq20$ote$1@smc.vnet.net>

I don't know what your problem with using Length is, but if you really need a specific test function you can easily roll it yourself: indexQ[index_Integer, list_List] := index <= Length[list] Cheers -- Sjoerd On Sep 26, 8:43 am, Joseph Gwinn <joegw... at comcast.net> wrote: > I have an application where I am bouncing around in a list, and may > accidentally ask for an element beyond the end of the list, which causes > Mathematica to complain and balk, preventing completion. > > Is there any way to test for the existence of a list element without > provoking complaint or balking should the list item fail to exist? > > Many of the suggestions made offline in response to the above imply that > I wasn't clear enough, so here is some expansion: > > All the list operations like MemberQ tell you if a member of the list > has some property or not. But it does not solve the problem of telling > if a slot (part) exists or not. > > For instance: > > list={a, b, c, d}; x=list[[60]] > > Mathematica will complain that "list[[60]]" does not exist, which is true=