diff --git a/array_tools.py b/array_tools.py
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+#
+# Created: 20140207
+# Wirawan Purwanto
+#
+
+"""
+wpylib.array_tools
+
+Various tools for arrays (mainly, numpy array objects).
+
+"""
+
+
+def array_indices_cond_1d(arr, cond):
+  """Get the odered list of array indices whose corresponding elements satisfy
+  a given condition.
+  Useful for conditional assignment or evaluation.
+
+  The input `cond' argument can be an ufunc-like function that evaluates
+  a logical expression in bulk for each of the arr's element.
+  Or it can be an array of logical values that has the same length as arr.
+
+  Example use case:
+
+     r = numpy.linspace(1.97, 3.5, num=150)
+     i_select = cond_indices_1d(r, r <= 2.5)
+     # ... then we can do something with r[i_select]
+     # for conditional assignment or value extraction.
+  """
+  arr = numpy.asarray(arr)
+  assert len(arr.shape) == 1
+
+  if callable(cond):
+    cond = cond(arr)
+  # otherwise, assume cond is already a good array
+  return numpy.array(xrange(len(arr)))[ cond ]
+
+
+
+