Initial commit

Solutions/2_6/colreader.py

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+# colreader.py
+
+import collections
+import csv
+
+class DataCollection(collections.Sequence):
+    def __init__(self, columns):
+        self.column_names = list(columns)
+        self.column_data = list(columns.values())
+
+    def __len__(self):
+        return len(self.column_data[0])
+
+    def __getitem__(self, index):
+        return dict(zip(self.column_names,
+                        (col[index] for col in self.column_data)))
+
+
+def read_csv_as_columns(filename, types):
+    columns = collections.defaultdict(list)
+    with open(filename) as f:
+        rows = csv.reader(f)
+        headers = next(rows)
+        for row in rows:
+            for name, func, val in zip(headers, types, row):
+                columns[name].append(func(val))
+            
+    return DataCollection(columns)
+
+if __name__ == '__main__':
+    import tracemalloc
+    from sys import intern
+
+    tracemalloc.start()
+    data = read_csv_as_columns('../../Data/ctabus.csv', [intern, intern, intern, int])
+    print(tracemalloc.get_traced_memory())
+

Solutions/2_6/cta.py

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+# cta.py
+
+from collections import defaultdict, Counter
+import tracemalloc
+import csv
+import sys
+
+tracemalloc.start()
+
+if True:
+    # Part (b)
+    import reader
+    rows = reader.read_csv_as_dicts('../../Data/ctabus.csv',
+                                    [sys.intern, sys.intern, sys.intern, int])
+else:
+    # Part (d) - Challenge
+    import colreader
+    rows = colreader.read_csv_as_columns('../../Data/ctabus.csv', 
+                                         [sys.intern, sys.intern, sys.intern, int])
+
+# --------------------------------------------------
+# Question 1:  How many bus routes are in Chicago?
+# Solution: Use a set to get unique values. 
+
+routes = set()
+for row in rows:
+    routes.add(row['route'])
+print(len(routes), 'routes')
+
+# --------------------------------------------------
+# Question 2: Total number of rides per route
+# Solution: Use a counter to tabulate things
+rides_per_route = Counter()
+for row in rows:
+    rides_per_route[row['route']] += row['rides']
+
+# Make a table showing the routes and a count ranked by popularity
+for route, count in rides_per_route.most_common():
+    print('%5s %10d' % (route, count))
+
+# --------------------------------------------------
+# Question 3: Routes with greatest increase in ridership 2001 - 2011
+# Solution: Counters embedded inside a defaultdict
+
+rides_by_year = defaultdict(Counter)
+for row in rows:
+    year = row['date'].split('/')[2]
+    rides_by_year[year][row['route']] += row['rides']
+
+diffs = rides_by_year['2011'] - rides_by_year['2001']
+for route, diff in diffs.most_common(5):
+    print(route, diff)
+
+# ---- Memory use
+print('Memory Use: Current %d, Peak %d' % tracemalloc.get_traced_memory())

Solutions/2_6/reader.py

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+# reader.py
+
+import csv
+
+def read_csv_as_dicts(filename, types):
+    '''
+    Read a CSV file into a list of dicts with column type conversion
+    '''
+    records = []
+    with open(filename) as f:
+        rows = csv.reader(f)
+        headers = next(rows)
+        for row in rows:
+            record = { name: func(val) for name, func, val in zip(headers, types, row) }
+            records.append(record)
+    return records
+
+        
+
+    
+
+