Merge pull request #23 from tmck-code/20241128_comparing_lists_or_mat…

…rices

20241128 comparing lists or matrices

README.md

@@ -4,6 +4,10 @@ my blog
 
 ---
 
+### [20241128 Comparing Lists or Matrices](articles/20241128_comparing_lists_or_matrices/20241128_comparing_lists_or_matrices.md)
+
+> _Functional approaches to compare sequences in Python_
+
 ### [20240829 Using JQ with style](articles/20240829_using_jq_with_style/20240829_using_jq_with_style.md)
 
 > _Colour/theme configuration for jq_

articles/20241128_comparing_lists_or_matrices/20241128_comparing_lists_or_matrices.md

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+# 20241128 Comparing Lists or Matrices
+
+Recently I needed to compare matrices (or "lists of lists"), counting the number of different items. I challenged myself to
+use the standard library instead of numpy.
+
+---
+
+These matrices have 2 differing values:
+
+```python
+m1 = [(0,0),
+      (0,1),]
+
+m2 = [(0,1),
+      (0,0),]
+```
+
+Firstly, it would be easiest (for me) if I somehow transformed each matrix into a single sneuence of numbers.
+This can be done using `chain` from the `itertools` standard library tools, which is one of my favourite and probably overused hacks.
+
+```python
+from itertools import chain
+
+list(chain.from_iterable(m1))
+# [0, 0, 0, 1]
+
+list(chain.from_iterable(m2))
+# [0, 1, 0, 0]
+```
+
+Using `zip`, we can iterate through both lists and compare each pair of elements:
+
+```python
+list(zip(
+    chain.from_iterable(m1),
+    chain.from_iterable(m2)
+))
+# [(0, 0), (0, 1), (0, 0), (1, 0)]
+```
+
+Next, we need to compare each pair of elements, and I thought of using the `operator` functions, as there is `ne` which could be used to compare elements.
+
+The documentation for `ne` is:
+
+> `ne(a, b, /)` *Same as a != b.*
+
+I want to avoid using a lambda as it is both icky and slow, e.g.
+
+```python
+list(map(
+    lambda x: x[0]==x[1],
+    zip(
+        chain.from_iterable(m1),
+        chain.from_iterable(m2)
+    )
+))
+# [True, False, True, False]
+```
+
+I can use `starmap` to take each pair, and pass it to `operator.eq` as `*args` (hence the name "starmap"! very cool 😎)
+
+```python
+from itertools import starmap
+
+list(starmap(
+    operator.ne,
+    zip(
+        chain.from_iterable(m1),
+        chain.from_iterable(m2)
+    )
+))
+# [True, False, True, False]
+```
+
+And finally, `sum` can be used to count the number of `True`/truthy results
+
+```python
+sum(starmap(
+    operator.ne,
+    zip(
+        chain.from_iterable(m1),
+        chain.from_iterable(m2)
+    )
+))
+# 2
+```
+
+> *Note: counting identical elements could be done easily by using `operator.eq` instead of `operator.ne`*