Join lines and arcs into polylines, gaps allowed

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;;; ============================================================================
;;; CXJOIN - Join lines and arcs into polylines, gaps allowed
;;; Version 1.0.0
;;; CADXChange LISP tools - https://cadxchange.net/resources/lisp/cxjoin
;;; Tested in: AutoCAD (full version). Other programs that run AutoLISP may work but are not tested.
;;; Copyright (c) CADXChange. Free for personal and commercial use; do not resell or
;;; republish it as a collection. Terms: https://cadxchange.net/legal/lisp-terms
;;; ============================================================================

;; Join the lines, arcs and polylines in NAMES into polylines, bridging gaps up to FUZZ.
;; PEDITACCEPT must be 1 so that lines and arcs convert without a question.
(defun cx:join-run (names fuzz / ss)
  (setq ss (ssadd))
  (foreach e names (ssadd e ss))
  (command "_.PEDIT" "_M" ss "" "_J" fuzz "")
  (princ))

(defun c:CXJOIN ( / *error* cx:sv ss fuzz before)
  (setq *error* cx:err)
  (if (setq ss (cx:pick "\nSelect lines, arcs and polylines to join: " '((0 . "LINE,ARC,LWPOLYLINE"))))
    (progn
      (setq fuzz   (cx:ask-real "Join gaps up to this distance (0 for exact ends only)" 0.0)
            before (sslength ss))
      (cx:start '(("CMDECHO" . 0) ("PEDITACCEPT" . 1)))
      (cx:join-run (cx:ss->list ss) fuzz)
      (princ (strcat "\nJoined " (itoa before) " selected object(s)."))
      (cx:end)))
  (princ))


;;; ---- Shared helpers (used by the command above; identical in every CADXChange tool) ----

;; Close the undo step and put the system variables back.
(defun cx:end ()
  (foreach v cx:sv (setvar (car v) (cdr v)))
  (command "_.UNDO" "_End")
  (setq cx:sv nil)
  (princ))

;; Error handler: restores everything, stays quiet on Esc.
(defun cx:err (msg)
  (if (> (getvar "CMDACTIVE") 0) (command))
  (cx:end)
  (if (and msg (not (wcmatch (strcase msg) "*BREAK*,*CANCEL*,*EXIT*")))
    (princ (strcat "\nError: " msg)))
  (princ))

;; Use the objects already selected, or ask the user to select; FILTER is an ssget filter list or nil.
(defun cx:pick (msg filter / ss)
  (setq ss (if filter (ssget "_I" filter) (ssget "_I")))
  (if (null ss)
    (progn
      (princ msg)
      (setq ss (if filter (ssget filter) (ssget)))))
  ss)

;; Real X as text with at most PREC decimals and no trailing zeros ("2.50" -> "2.5", "3.00" -> "3").
(defun cx:num (x prec / s)
  (setq s (rtos x 2 prec))
  (if (wcmatch s "*.*")
    (progn
      (while (= (substr s (strlen s)) "0") (setq s (substr s 1 (1- (strlen s)))))
      (if (= (substr s (strlen s)) ".") (setq s (substr s 1 (1- (strlen s)))))))
  (if (or (= s "-0") (= s "")) "0" s))

(defun cx:ask-real (msg def / v)
  (setq v (getreal (strcat "\n" msg " <" (cx:num def 6) ">: ")))
  (if v v def))

;; Save the system variables in VARS ((name . value) ...), set them, and open one undo step.
;; The caller declares cx:sv as a local so the saved values live exactly as long as the command.
(defun cx:start (vars)
  (setq cx:sv (mapcar (function (lambda (v) (cons (car v) (getvar (car v))))) vars))
  (command "_.UNDO" "_Begin")
  (foreach v vars (setvar (car v) (cdr v)))
  (princ))

;; Selection set to a list of entity names.
(defun cx:ss->list (ss / i out)
  (setq i 0)
  (if ss
    (repeat (sslength ss)
      (setq out (cons (ssname ss i) out)
            i   (1+ i))))
  (reverse out))

(princ "\nCXJOIN loaded. Type CXJOIN to start.")
(princ)

More commands: Measuring and polylines

• CXAREAWrite the area inside closed shapes
• CXLENWrite the length along lines, arcs and polylines
• CXSUMTotal length and area by layer
• CXCENTROIDFind and mark the centre of closed shapes
• CXDISTMeasure a path point by point
• CXPLCLOSEClose polylines whose ends almost meet
• CXPLREVReverse the direction of lines and polylines
• CXPLCLEANRemove duplicate and straight-line vertices
• CXPLWIDTHSet one width for many polylines