Add bifurcate_by snippet

snippets/bifurcate_by.md

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+---
+title: bifurcate_by
+tags: list,function,intermediate
+---
+
+Splits values into two groups according to a function, which specifies which group an element in the input list belongs to. 
+If the function returns `True`, the element belongs to the first group; otherwise, it belongs to the second group.
+
+Use list comprehension to add elements to groups, based on `fn`.
+
+```py
+def bifurcate_by(lst, fn):
+  return [
+    [x for x in lst if fn(x)],
+    [x for x in lst if not fn(x)]
+  ]
+```
+
+```py
+bifurcate_by(['beep', 'boop', 'foo', 'bar'], lambda x: x[0] == 'b') # [ ['beep', 'boop', 'bar'], ['foo'] ]
+```