All tests pass

.gitignore

@@ -65,3 +65,4 @@ target/
 # Temporary data
 .ipynb_checkpoints/
 
+extract_functions.py

matrix_math.py

@@ -1,2 +1,119 @@
+import functools
+import math
+
+
 class ShapeException(Exception):
     pass
+
+
+def shape(array):
+    """Take a vector or matrix and return a tuple with the
+    number of rows (for a vector) or the number of rows and columns
+    (for a matrix.)"""
+    try:
+        return (len(array), len(array[0]))
+    except TypeError:
+        return (len(array),)
+
+
+def vector_walk(x, y, op=sum, filter=lambda x_, y_: True):
+    if shape(x) != shape(y):
+        raise ShapeException
+    try:
+        return [op([x_val, y[idx_r][idx_c]])
+                for idx_r, row in enumerate(x)
+                for idx_c, x_val in row
+                if filter(idx_r, idx_c)
+                ]
+    except TypeError:
+        return [op([x_val, y[idx_r]]) for idx_r, x_val in enumerate(x)]
+
+
+def sub(a_list):
+    if len(a_list) != 2:
+        raise ShapeException
+    return a_list[0] - a_list[1]
+
+
+def times(a_list):
+    if len(a_list) != 2:
+        raise ShapeException
+    return a_list[0] * a_list[1]
+
+
+def is_equal(idx_x, idx_y):
+    return idx_x == idx_y
+
+
+def vector_add(x, y):
+    return vector_walk(x, y, op=sum)
+
+
+def vector_sub(x, y):
+    return vector_walk(x, y, op=sub)
+
+
+def vector_sum(*vectors):
+    return functools.reduce(vector_add, vectors)
+
+
+def dot(x, y):
+    return sum(vector_walk(x, y, op=times, filter=is_equal))
+
+
+def vector_multiply(x, scalar):
+    scalar_matrix = vector_walk(x, x, op=lambda x_: scalar)
+    return vector_walk(x, scalar_matrix, op=times)
+
+
+def vector_mean(*vectors):
+    sum_vector = vector_sum(*vectors)
+    n = len(vectors)
+    return vector_multiply(sum_vector, 1 / n)
+
+
+def magnitude(x):
+    return math.sqrt(dot(x, x))
+
+
+def matrix_row(x, n):
+    return x[n]
+
+
+def matrix_col(x, n):
+    return [val for row in x for idx, val in enumerate(row) if idx == n]
+
+
+def matrix_cols(x):
+    for col in [val for row in x for idx, val in enumerate(row)]:
+        yield col
+
+
+def matrix_scalar_multiply(matrix, scalar):
+    return [[i*scalar for i in row] for row in matrix]
+
+
+def matrix_vector_multiply(matrix, vector):
+    if shape(matrix)[1] != shape(vector)[0]:
+        raise ShapeException
+
+    step1 = [[val * vector[idx] for idx, val in enumerate(row)]
+             for row in matrix]
+    return [sum(x) for x in step1]
+
+
+def matrix_matrix_multiply(x, y):
+    if shape(x)[1] != shape(y)[0]:
+        raise ShapeException
+
+    y_transposed = [[row[i] for row in y] for i in range(len(y[0]))]
+
+    return [[dot(row, col) for col in y_transposed] for row in x]
+
+    # return [[dot(matrix_row(x, j), matrix_row(y_transposed, i))
+    #         for i, val in enumerate(row)]
+    #         for j, row in enumerate(x)]
+
+    # return [[dot(row, val) for i,val in enumerate(matrix_cols(y))
+    #        if j < len(y)]
+    #        for j, row in enumerate(x)]

test_matrix_math.py

@@ -218,7 +218,7 @@ def test_matrix_matrix_multiply():
 
     Matrix * Matrix = Matrix
     """
-    assert matrix_matrix_multiply(A, B) == A
+    assert matrix_matrix_multiply(A, B) == B
     assert matrix_matrix_multiply(B, C) == [[8, 10],
                                             [20, 25],
                                             [32, 40]]