Get index of list within list in Lisp

Question

If I have a list like this

((0 1 2) (3 4 5) (6 7 8) (0 3 6) (1 3 7) (2 4 8) (0 4 8) (2 4 6))

And I want to find the index of (0 3 6), is there a built-in function to do this? POSITION doesn't seem to work when the search item is itself a list.

Nietzche-jou · Accepted Answer · 2010-11-26 20:22:10Z

14

See hyperspec. POSITION can take a :test argument:

(position '(0 3 6)
          '((0 1 2) (3 4 5) (6 7 8) (0 3 6) (1 3 7) (2 4 8) (0 4 8) (2 4 6))
          :test #'equal))
3

The default test for POSITION (and other sequence operations) is EQL, by the way.

edited Nov 26, 2010 at 20:22

answered Nov 26, 2010 at 20:15

Nietzche-jou

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2 Comments

Ken Over a year ago

Curiously, the CLHS page for FIND links to "Rules about Test Functions", but the page for POSITION doesn't. Here's where the default of EQL is documented: lispworks.com/documentation/HyperSpec/Body/17_ba.htm

Ala Aga Over a year ago

sorry but which language should i choose in DrRacket to run this code @Nietzche-jou

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