Counting with a Dictionary
~10 mincode completion
Write count_labels(labels) that takes a list of labels and returns a dictionary mapping each label to how many times it appeared.
["cat", "dog", "cat"] returns {"cat": 2, "dog": 1}.
Examples
Repeated labels are counted, not overwritten
- Input
- count_labels(["cat", "dog", "cat"])
- Output
- {"cat": 2, "dog": 1}
Every label appearing once gives every count as 1
- Input
- count_labels(["a", "b", "c"])
- Output
- {"a": 1, "b": 1, "c": 1}
One label repeated is counted correctly
- Input
- count_labels(["spam", "spam", "spam", "spam"])
- Output
- {"spam": 4}
Hints
Hint 1
A dictionary keyed by the value counts occurrences in one pass.
Hint 2
A common slip here: overwrote instead of incremented.
Requirements
labels: a list of stringsReturn a dict mapping label -> count.
Constraints
Standard library only, no imports required
Time limit: 200 ms, Memory: 64 MB
Where this shows up
~10 min
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Python
def count_labels(labels):
"""
Count how many times each label appears.
Args:
labels: a list of strings
Returns:
A dict mapping label -> count.
"""
# YOUR CODE HERE
pass