fixed issue #894

Author: MgeeeeK

libpysal/weights/util.py

@@ -114,41 +114,34 @@ def hexLat2W(nrows=5, ncols=5, **kwargs):
     return W(w, **kwargs)
 
 
-def lat2W(nrows=5, ncols=5, rook=True, id_type='int', **kwargs):
+def lat2W(nrows=5, ncols=5, rook=True, torus=False, id_type='int', **kwargs):
     """
     Create a W object for a regular lattice.
-
     Parameters
     ----------
-
     nrows      : int
                  number of rows
     ncols      : int
                  number of columns
     rook       : boolean
                  type of contiguity. Default is rook. For queen, rook =False
+    torus       : boolean
+                 generates weights for circles, spheres. Default is set to False
     id_type    : string
                  string defining the type of IDs to use in the final W object;
                  options are 'int' (0, 1, 2 ...; default), 'float' (0.0,
                  1.0, 2.0, ...) and 'string' ('id0', 'id1', 'id2', ...)
     **kwargs   : keyword arguments
                  optional arguments for :class:`pysal.weights.W`
-
-
     Returns
     -------
-
     w : W
         instance of spatial weights class W
-
     Notes
     -----
-
     Observations are row ordered: first k observations are in row 0, next k in row 1, and so on.
-
     Examples
     --------
-
     >>> from libpysal.weights import lat2W
     >>> w9 = lat2W(3,3)
     >>> "%.3f"%w9.pct_nonzero
@@ -161,11 +154,11 @@ def lat2W(nrows=5, ncols=5, rook=True, id_type='int', **kwargs):
     n = nrows * ncols
     r1 = nrows - 1
     c1 = ncols - 1
+    lat_pts = range(n)
     rid = [i // ncols for i in range(n)] #must be floor!
     cid = [i % ncols for i in range(n)]
     w = {}
-    r = below = 0
-    for i in range(n - 1):
+    for i in range(n):
         if rid[i] < r1:
             below = rid[i] + 1
             r = below * ncols + cid[i]
@@ -187,6 +180,38 @@ def lat2W(nrows=5, ncols=5, rook=True, id_type='int', **kwargs):
                 r = (rid[i] + 1) * ncols - 1 + cid[i]
                 w[i] = w.get(i, []) + [r]
                 w[r] = w.get(r, []) + [i]
+        if torus:
+            if rid[i] == r1 and r1 not in [0, 1]:
+                below = rid[i] + 1
+                r = lat_pts[(below * ncols + cid[i]) - n]
+                w[i] = w.get(i, []) + [r]
+                w[r] = w.get(r, []) + [i]
+            if cid[i] == c1 and c1 not in [0, 1]:
+                c = lat_pts[(rid[i] * ncols) - n]
+                w[i] = w.get(i, []) + [c]
+                w[c] = w.get(c, []) + [i]
+            if not rook:
+                if  r1 not in [0, 1]:
+                    # southeast bishop
+                    if cid[i] < c1 and rid[i] == r1:
+                        r = lat_pts[((rid[i] + 1) * ncols + 1 + cid[i]) - n]
+                        w[i] = w.get(i, []) + [r]
+                        w[r] = w.get(r, []) + [i]
+                    # southwest bishop 
+                    if cid[i] > 0 and rid[i] == r1:
+                        r = lat_pts[((rid[i] + 1) * ncols - 1 + cid[i]) - n]
+                        w[i] = w.get(i, []) + [r]
+                        w[r] = w.get(r, []) + [i]
+                if  c1 not in [0, 1]:
+                    if cid[i] == c1:
+                        r = lat_pts[i + 1 - n]
+                        w[i] = w.get(i, []) + [r]
+                        w[r] = w.get(r, []) + [i]
+                    if cid[i] == 0:
+                        below = rid[i] + 2
+                        r = lat_pts[(below * ncols - 1) - n]
+                        w[i] = w.get(i, []) + [r]
+                        w[r] = w.get(r, []) + [i]
 
     neighbors = {}
     weights = {}
@@ -211,6 +236,7 @@ def lat2W(nrows=5, ncols=5, rook=True, id_type='int', **kwargs):
     return W(w, weights, ids=ids, id_order=ids[:], **kwargs)
 
 
+
 def block_weights(regimes, ids=None, sparse=False, **kwargs):
     """
     Construct spatial weights for regime neighbors.