I have a 2D list that contains soccer player names, the number of times they scored a goal, and the number of times they attempted a shot on goal, respectively.
player_stats = [['Adam', 5, 10], ['Kyle', 12, 18], ['Jo', 20, 35], ['Adam', 15, 20], ['Charlie', 31, 58], ['Jo', 6, 14], ['Adam', 10, 15]]
From this list, I'm trying to return another list that shows only one instance of each player with their respective total goals and total attempts on goal, like so:
player_stats_totals = [['Adam', 30, 45], ['Kyle', 12, 18], ['Jo', 26, 49], ['Charlie', 31, 58]]
After searching on Stack Overflow I was able to learn (from this thread) how to return the indexes of the duplicate players
x = [player_stats[i][0] for i in range (len(player_stats))]
for i in range (len(x)):
if (x[i] in x[:i]) or (x[i] in x[i+1:]): print (x[i], i)
but got stuck on how to proceed thereafter and if indeed this method is strictly relevant for what I need(?)
What's the most efficient way to return the desired list of totals?
Use a dictionary to accumulate the values for a given player:
player_stats = [['Adam', 5, 10], ['Kyle', 12, 18], ['Jo', 20, 35], ['Adam', 15, 20], ['Charlie', 31, 58], ['Jo', 6, 14], ['Adam', 10, 15]]
lookup = {}
for player, first, second in player_stats:
# if the player has not been seen add a new list with 0, 0
if player not in lookup:
lookup[player] = [0, 0]
# get the accumulated total so far
first_total, second_total = lookup[player]
# add the current values to the accumulated total, and update the values
lookup[player] = [first_total + first, second_total + second]
# create the output in the expected format
res = [[player, first, second] for player, (first, second) in lookup.items()]
print(res)
Output
[['Adam', 30, 45], ['Kyle', 12, 18], ['Jo', 26, 49], ['Charlie', 31, 58]]
A more advanced, and pythonic, version is to use a collections.defaultdict:
from collections import defaultdict
player_stats = [['Adam', 5, 10], ['Kyle', 12, 18], ['Jo', 20, 35],
['Adam', 15, 20], ['Charlie', 31, 58], ['Jo', 6, 14], ['Adam', 10, 15]]
lookup = defaultdict(lambda: [0, 0])
for player, first, second in player_stats:
# get the accumulated total so far
first_total, second_total = lookup[player]
# add the current values to the accumulated total, and update the values
lookup[player] = [first_total + first, second_total + second]
# create the output in the expected format
res = [[player, first, second] for player, (first, second) in lookup.items()]
print(res)
This approach has the advantage of skipping the initialisation. Both has approaches are O(n).
Notes
The expression:
res = [[player, first, second] for player, (first, second) in lookup.items()]
is a list comprehension, equivalent to the following for loop:
res = []
for player, (first, second) in lookup.items():
res.append([player, first, second])
Additionally, read this for understanding unpacking.
What you want to do is use a dictionary where the key is the player name and the value is a list containing [goals, shots]. Constructing it would look like this:
all_games_stats = {}
for stat in player_stats:
player, goals, shots = stat
if player not in all_games_stats:
all_games_stats[player] = [goals, shots]
else:
stat_list = all_games_stats[player]
stat_list[0] += goals
stat_list[1] += shots
Then, if you want to represent the players and their stats as a list, you would do: list(all_games_stats.items())
You can convert the list to a dictionary. (It can always be changed back once done) This works:
player_stats = [['Adam', 5, 10], ['Kyle', 12, 18], ['Jo',
20, 35], ['Adam', 15, 20], ['Charlie', 31, 58], ['Jo', 6,
14], ['Adam', 10, 15]]
new_stats = {}
for item in player_stats:
if not item[0] in new_stats:
new_stats[item[0]] = [item[1],item[2]]
else:
new_stats[item[0]][0] += item[1]
new_stats[item[0]][1] += item[2]
print(new_stats)