How to cut elements from set of data based on function restrictions? [duplicate]

Question

For example, say I have a set of data which takes the form

list = {{1,2,4,5,3,2},{2,3,4,2,1,6},{2,3,4,5,4,3}}

where all of the elements have a length of 6. Then I have to run this list through many functions each with various restrictions e.g.:

ptOf[event_]:=px+py/;(px+py)<4,

where px is the first element in the 6 vector {px,py,_,_,_,_} and py is the second element.

How would I cut the elements from the original list that do not satisfy this condition?

I don't really get it but Select[list, #[[1]] + #[[2]] < 4 &]? — Öskå, Commented Jun 27, 2014 at 15:45
This is an extremely common class of question. In addition to the Linked questions under the original see also e.g. (11219), (11780), (30155), (33880). For clarity I would use: Cases[list, {a_, b_, ___} /; a + b < 4]. For speed choose numeric methods using e.g. UnitStep. — Mr.Wizard, Commented Jun 27, 2014 at 19:46

Öskå · Accepted Answer · 2014-06-27 16:20:20Z

1

For this special case you need to use Select and Part a.k.a. [[]]:

list = {{1,2,4,5,3,2},{2,3,4,2,1,6},{2,3,4,5,4,3}}  
Select[list, #[[1]] + #[[2]] < 4 &]

{{1, 2, 4, 5, 3, 2}}

answered Jun 27, 2014 at 16:20

Öskå

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