Warn when repacking arrays with non-float fields

The values in each non-float field will be converted to floats, which
may or may not be desirable. This is likely only sensible for, e.g.,
integer fields.

src/pypfilt/state.py

@@ -3,6 +3,7 @@
 import logging
 import numpy as np
 import numpy.lib.recfunctions
+import warnings
 
 
 def is_history_matrix(ctx, arr):
@@ -172,8 +173,23 @@ def earlier_states(hist, ix, steps):
 
 def repack(svec):
     """
-    Return a copy of the array ``svec`` where the fields are contiguous.
+    Return a copy of the array ``svec`` where the fields are contiguous and
+    viewed as a regular Numpy array of floats.
+
+    :raises UserWarning: if ``svec`` contains any non-float fields, each of
+        which will be converted to floats.
     """
     svec = numpy.lib.recfunctions.repack_fields(svec)
+    # Convert any non-float fields (e.g., integers) into floats.
+    cols = [(name, svec.dtype.fields[name][0]) for name in svec.dtype.names]
+    all_floats = all(np.issubdtype(col[1], float) for col in cols)
+    if not all_floats:
+        warnings.warn('Repacking array with non-float fields',
+                      stacklevel=2)
+        new_dtype = [
+            (col[0], col[1] if np.issubdtype(col[1], float) else float,
+             col[1].shape)
+            for col in cols]
+        svec = np.array(svec, dtype=new_dtype)
     svec = svec.view((float, len(svec.dtype.names)))
     return svec