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Here is my list coordinate {x,y,z}

list  = {{30.8179, -62.2833, -155.032}, {33.1172, -61.0918, -156.656},
         {35.3704, -59.8155, -158.28}, {37.5745, -58.456, -159.904},
         {39.7264, -57.0155, -161.528}, {41.8232, -55.4957, -163.152},
         {43.8619, -53.8989, -164.776}, {45.8397, -52.2272, -166.4}}

If I only knew the value of z coordinate only, e.g. 162.4 How to make programming in order to detect the nearest position or index with z value of 162.4?

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  • $\begingroup$ You've looked up Nearest[], no? $\endgroup$
    – J. M.'s missing motivation ♦
    Commented Nov 3, 2017 at 3:41
  • $\begingroup$ Since the z-coordinates in your example data are all negative, I suspect you meant you want the triple having z closest to -164.4. Is that right? $\endgroup$
    – m_goldberg
    Commented Nov 3, 2017 at 5:16
  • $\begingroup$ You mean -162.4 right? $\endgroup$
    – MCMastery
    Commented Nov 3, 2017 at 13:33

2 Answers 2

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Assuming that you want to find the element of list that is nearest to z = -162.4, it can be done like so:

Extract[list, Nearest[list[[All, 3]] -> "Index", -162.4]]

{41.8232, -55.4957, -163.152}

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  • $\begingroup$ I've apply it in version 10.3 but it's not worked. Is there any additional code? $\endgroup$
    – SelfA
    Commented Nov 3, 2017 at 6:21
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    $\begingroup$ @Self, try Extract[list, Nearest[list[[All, 3]] -> Automatic, -162.4]]. $\endgroup$
    – J. M.'s missing motivation ♦
    Commented Nov 3, 2017 at 7:08
  • $\begingroup$ Yeah, It works. $\endgroup$
    – SelfA
    Commented Nov 3, 2017 at 7:11
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To get the vector with the most similar z value:

Nearest[Last /@ list -> list, 162.4]
(* Out: {{30.8179, -62.2833, -155.032}} *)

To get the index of the same vector:

Nearest[Last /@ list -> Automatic, 162.4]
(* Out: {1} *)
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