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--- get_unique_items_in_a_list [2021/07/23 21:33] – created raju
+++ get_unique_items_in_a_list [2021/07/23 22:14] (current) – [Notes and assumptions] raju
@@ Line 1: / Line 1: @@
 ===== Get unique items in a list =====
 ==== Task ====
-Get the unique items from
+Given
 <code>
-['nowplaying', 'PBS', 'PBS', 'nowplaying', 'job', 'debate', 'thenandnow']
+mylist = ['nowplaying', 'PBS', 'PBS', 'nowplaying', 'job', 'debate', 'thenandnow']
 </code>
-This can be one of three ways:
+get the list of unique items. The output can be one of three ways:
   - Order does not matter. <code>
 ['thenandnow', 'debate', 'nowplaying', 'PBS', 'job']
 </code>
-  - Preserve the order. Keep the first unique one. <code>
+  - Preserve the order and keep the first unique item. <code>
 ['nowplaying', 'PBS', 'job', 'debate', 'thenandnow']
 </code>
-  - Preserve the order. Keep the last unique one. <code>
+  - Preserve the order and keep the last unique item. <code>
 ['PBS', 'nowplaying', 'job', 'debate', 'thenandnow']
 </code>
+==== Notes and assumptions ====
+  * Starting from Python 3.7, dictionaries in python are ordered by insertion order. Per https://docs.python.org/3.7/tutorial/datastructures.html#dictionaries <code>
+Performing list(d) on a dictionary returns a list of all the keys used in the dictionary, in insertion order
+</code>
+  * Assume Python >= 3.7 is used.
+==== Case 1: unique unordered ====
+<code>
+uniq_no_order = list(set(mylist))
+print(uniq_no_order)
+</code>
+<code>
+['nowplaying', 'job', 'debate', 'PBS', 'thenandnow']
+</code>
+==== Case 2: keep first unique ====
+<code>
+uniq_first = list({key:1 for key in mylist}.keys())
+print(uniq_first)
+</code>
+<code>
+['nowplaying', 'PBS', 'job', 'debate', 'thenandnow']
+</code>
+==== Case 3: keep last unique ====
+<code>
+uniq_last = list({key:1 for key in mylist[::-1]}.keys())[::-1]
+print(uniq_last)
+</code>
+<code>
+['PBS', 'nowplaying', 'job', 'debate', 'thenandnow']
+</code>