Mapcar and Lambda Exercises

I am trying to make myself familiar with the LAMBDA and MAPCAR commands and I have specific task which I'd like to try it out on.

I have a list containing 8 points, ( pt1 pt2...pt8 ). I want to write a function which will draw a cross shape (+) 1" long in each direction, with it's center on each of the eight points.

I assigned the variables as follows:

(setq pt1 '(0.0 0.0)
   pt2 (polar pt1 (dtr 0.0) a)
   pt3 (polar pt2 (dtr 270.0) b)
   pt4 (polar pt1 (dtr 270.0) b)
   pt5 (polar pt2 (dtr 180.0) (+ b 36))
   pt6 (polar pt5 (dtr 270.0) a)
   pt7 (polar pt4 (dtr 270.0) 36)
   pt8 (polar pt7 (dtr 0.0) b)

Variables 'a' and 'b' are assigned elsewhere to set the distances between the points. I then tried this:

(setq aa '(pt1 pt2 pt3 pt4 pt5 pt6 pt7 pt8))

 (mapcar 
   
 (command "._LINE" (polar aa (dtr 90.0) 0.5) (polar aa (dtr 270.0) 0.5) "")
 (command "._LINE" (polar aa (dtr 180.0) 0.5) (polar aa (dtr 270.0) 0.5) "")
 )

(dtr) is the standard degrees to radian function.

Please check if this what you are looking for:

(mapcar
(function (lambda(p) (command "_LINE" (polar p (dtr  90.0) 0.5) (polar p (dtr 270.0) 0.5) ""
                              "_LINE" (polar p (dtr 180.0) 0.5) (polar p (dtr 270.0) 0.5) "")))
aa)

if variable aa is a list of variable names

(mapcar
(function (lambda (p) (command "_LINE" (polar p (dtr  90.0) 0.5) (polar p (dtr 270.0) 0.5) ""
                              "_LINE" (polar p (dtr 180.0) 0.5) (polar p [color=blue][b]0[/b][/color] 0.5) "")))
([b][color=blue]mapcar[/color][/b] 'eval [color=blue][b]aa[/b][/color]))

Besides, this sample is a not a good way to show what mapcar can do. and its more than just creating a list.

what do you have in mind?

for example. i want to create a list of the points the "+" shapes

(setq all (mapcar
(function (lambda (p / [b][color=blue]w x y z[/color][/b]) (command "_LINE" [color=blue](setq w ([/color]polar p (dtr  90.0) 0.5)[color=blue])[/color]
                                                 [color=blue](setq x[/color] (polar p (dtr 270.0) 0.5)[color=blue])[/color] ""
                               "_LINE" [color=blue](setq y[/color] (polar p (dtr 180.0) 0.5)[color=blue])[/color]
                                      [color=blue] (setq z[/color] (polar p 0 0.5)[color=blue])[/color] "") [color=blue][b](list w x y z)[/b][/color]))
(mapcar 'eval aa)))

if im not going to utilize the resulting list, i might as well use foreach

(foreach p (mapcar 'eval aa)
(command "_LINE" (polar p (dtr  90.0) 0.5) (polar p (dtr 270.0) 0.5) ""
                              "_LINE" (polar p (dtr 180.0) 0.5) (polar p 0 0.5) ""))

FWIW - Lee already has some great tutorials on Mapcar & Lambda, and I found this Autodesk University course to be helpful when first tackling the Apply, Mapcar, and Lambda functions.

** Note - CADTutor will not allow PDF's over 500 KB, so I've added a .DWG file extension (which allows 1000 KB), simply remove .DWG and open the resultant .PDF file.

HTH

CP304-1-Handout-.pdf.dwg

@RenderMan: Thas seems a really great course, especially the part on recursion. Thank you for sharing!

Anytime, Mircea.

..... simply remove .DWG and open the resultant .PDF file.

HTH

sometime ago somebody pointed me to that same handout. it helped me a lot to understand lambda . Didnt go far with recursive though ..

Renderman , file can't be opened . even on cad 2012

Thanks

Renderman , file can't be opened . even on cad 2012

 

Thanks

Read the Rendermans note tharwat

Read the Rendermans note tharwat

Thank you mate .

just got it .

Thank you Renderman , that's a very generous post from you.

Highly appreciated.

Happy to help guys, I hope you can put the course materials to good use.

It's just a shame that Autodesk keeps removing course year(s) from the online course database... I guess I'll just have to keep downloading each-and-every-course that I find useful.

DTR function if standard angles then why not

put in startup lisp
(setq pi45 0.7853981634)
(setq pi90 1.57070796327)
(setq pi180 3.141592654)
(setq pi270 4.71238898)

(setq pt3 (polar pt1 pi90 x)) 

For Accuracy

(/ pi 4.0 ) ;--> 45
(/ pi 2.0) ;--> 90
(* pi 1.5) ;--> 270
pi    ;--> 180

DTR function if standard angles then why not

 

put in startup lisp
(setq pi45 0.7853981634)
(setq pi90 1.57070796327)
(setq pi180 3.141592654)
(setq pi270 4.71238898)

(setq pt3 (polar pt1 pi90 x)) 

For Accuracy

 

(/ pi 4.0 ) ;--> 45
(/ pi 2.0) ;--> 90
(* pi 1.5) ;--> 270
pi    ;--> 180

X1! Much more efficient & less typing & easier to read.

Or this:

(setq tmp 45)
(repeat 6
 (set (read (strcat "pi" (itoa tmp))) (* (/ tmp 180.) pi))
 (setq tmp (+ tmp 45)))
(setq tmp nil)