Min. z value of some points

niccah

Hi!

I have lots of 3D points: points = [[1, 2, 3], [2, 3, 5], ...]

Is there a easy way to get for example the minimum z value of all these points in Ruby?

At the moment I have a points.each loop and compare every z value with the last one....

Thanks for your help!

thomthom

min = points.inject(0) { |m,pt| ( pt.z < m ) ? pt.z : m }

Inject have many neat usages - I noted a couple of examples: http://forums.sketchucation.com/viewtopic.php?t=41176&p=364915

thomthom

Haven't checked if it is faster, but BoundingBox might help:

<span class="syntaxdefault">bb </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> Geom</span><span class="syntaxkeyword">;;</span><span class="syntaxdefault">BoundingBox</span><span class="syntaxkeyword">.new<br /></span><span class="syntaxdefault">bb</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">add</span><span class="syntaxkeyword">(</span><span class="syntaxdefault"> points </span><span class="syntaxkeyword">)<br /></span><span class="syntaxdefault">min </span><span class="syntaxkeyword">=</span><span class="syntaxdefault"> bb</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">min</span><span class="syntaxkeyword">.</span><span class="syntaxdefault">z</span>

Since it's SU's native code doing the handling of the points, it might yield faster calculations.

niccah

oh thank you very much!

I saw the function "inject", but I ignored them because I thought, that's not interesting for me.

Just for the sake of completeness: One have to add a "Geom::" in the front of "BoundingBox.new"

Thanks a lot again for your help!

br

thomthom

@niccah said:

Just for the sake of completeness: One have to add a "Geom::" in the front of "BoundingBox.new"

Good catch! Updated the example.

fredo6

to be absolutely accurate, I guess the inject statement should be

min = points.inject(points[0].z) { |m,pt| ( pt.z < m ) ? pt.z : m }

Fredo

PS: Did not know this method, as it is not documented in the Pragmatic Programmer's guide. Seems useful and elegant

Dan Rathbun

@unknownuser said:

PS: Did not know this method, as it is not documented in the Pragmatic Programmer's guide. Seems useful and elegant

Do not use the object reference from that OLD guide, which was written in the Ruby v 1.6.x timeframe. (The tutorial text is still relevant and recommended, however.)

Instead use the v 1.8.6 CHM here

or access on-line http://www.ruby-doc.org/core-1.8.6/index.html.

Note that these methods come from the mixin module Enumerable which is mixed into Array, Hash, IO (and subclasses, such as File,) Range, String, Struct, ... etc.

Dan Rathbun

@unknownuser said:

to be absolutely accurate, I guess the inject statement should be

min = points.inject(points[0].z) { |m,pt| ( pt.z < m ) ? pt.z : m }

At, one time, in another thread, we were comparing various methods of getting min and max, speedwise.

There is also:

min_z = points.min {|a,b| a.z <=> b.z }

Can't remember which was the faster.

P.S.: Because min and max are method names in Enumerable, and that they are mixed into quite a few classes, .. it is recommended to not use them as var names.
Difference them. It seems that the API's tradition is to add an "_" and then a descriptor: min_x, min_y, min_z, min_height, min_width, min_size, etc.

niccah

This forum is amazing!

I learn a lot from you! Thanks a lot for all these information!

david.

This is how I would do it:

minZ = points.collect { |pt| pt.z }.min

Dan Rathbun

@david: Your example should be slower, as it must iterate 2 arrays, and also create a temporary array.

Why ?? (I suspect you like the "readability" of your version.)

david.

Yes, readability. If it was operating on large quantities of data, I would definitely use your suggested method.