MAINT: Split thresholding.threshold

Each mode of the threshold function was independent, so they make more sense as
individual functions. This commit is just a code rearrangement, no change to
functionality.

Addresses PyWavelets#61

pywt/thresholding.py

@@ -14,6 +14,39 @@
 
 import numpy as np
 
+def soft(data, value, substitute=0):
+    data = np.asarray(data)
+    mvalue = -value
+
+    cond_less = np.less(data, value)
+    cond_greater = np.greater(data, mvalue)
+
+    output = np.where(cond_less & cond_greater, substitute, data)
+    output = np.where(cond_less, output + value, output)
+    output = np.where(cond_greater, output - value, output)
+    return output
+
+def hard(data, value, substitute=0):
+    data = np.asarray(data)
+    mvalue = -value
+
+    cond = np.less(data, value)
+    cond &= np.greater(data, mvalue)
+
+    return np.where(cond, substitute, data)
+
+def greater(data, value, substitute=0):
+    data = np.asarray(data)
+    return np.where(np.less(data, value), substitute, data)
+
+def less(data, value, substitute=0):
+    data = np.asarray(data)
+    return np.where(np.greater(data, value), substitute, data)
+
+thresholding_options = {'soft': soft,
+                        'hard': hard,
+                        'greater': greater,
+                        'less': less}
 
 def threshold(data, value, mode='soft', substitute=0):
     """
@@ -67,34 +100,9 @@ def threshold(data, value, mode='soft', substitute=0):
     array([ 1. ,  1.5,  2. ,  0. ,  0. ,  0. ,  0. ])
 
     """
-    data = np.asarray(data)
-
-    if mode == 'soft':
-        mvalue = -value
-
-        cond_less = np.less(data, value)
-        cond_greater = np.greater(data, mvalue)
-
-        output = np.where(cond_less & cond_greater, substitute, data)
-        output = np.where(cond_less, output + value, output)
-        output = np.where(cond_greater, output - value, output)
-
-    elif mode == 'hard':
-        mvalue = -value
 
-        cond = np.less(data, value)
-        cond &= np.greater(data, mvalue)
-
-        output = np.where(cond, substitute, data)
-
-    elif mode == 'greater':
-        output = np.where(np.less(data, value), substitute, data)
-
-    elif mode == 'less':
-        output = np.where(np.greater(data, value), substitute, data)
-
-    else:
+    try:
+        return thresholding_options[mode](data, value, substitute)
+    except KeyError:
         raise ValueError("The mode parameter only takes value among "
                          "{'soft', 'hard', 'greater','less'}.")
-
-    return output