问题
I am looking for a faster way to load data from my json object into a multiindex dataframe.
My JSON is like:
{
"1990-1991": {
"Cleveland": {
"salary": "$14,403,000",
"players": {
"Hot Rod Williams": "$3,785,000",
"Danny Ferry": "$2,640,000",
"Mark Price": "$1,400,000",
"Brad Daugherty": "$1,320,000",
"Larry Nance": "$1,260,000",
"Chucky Brown": "$630,000",
"Steve Kerr": "$548,000",
"Derrick Chievous": "$525,000",
"Winston Bennett": "$525,000",
"John Morton": "$350,000",
"Milos Babic": "$200,000",
"Gerald Paddio": "$120,000",
"Darnell Valentine": "$100,000",
"Henry James": "$75,000"
},
"url": "https://hoopshype.com/salaries/cleveland_cavaliers/1990-1991/"
},
I am making the dataframe like:
df = pd.DataFrame(columns=["year", "team", "player", "salary"])
for year in nbaSalaryData.keys():
for team in nbaSalaryData[year]:
for player in nbaSalaryData[year][team]['players']:
df = df.append({
"year": year,
"team": team,
"player": player,
"salary": nbaSalaryData[year][team]['players'][player]
}, ignore_index=True)
df = df.set_index(['year', 'team', 'player']).sort_index()
df
Which results in:
salary
year team player
1990-1991 Atlanta Doc Rivers $895,000
Dominique Wilkins $2,065,000
Gary Leonard $200,000
John Battle $590,000
Kevin Willis $685,000
... ... ... ...
2020-2021 Washington Robin Lopez $7,300,000
Rui Hachimura $4,692,840
Russell Westbrook $41,358,814
Thomas Bryant $8,333,333
Troy Brown $3,372,840
This is the form I want - year, team, and player as indexes and salary as a column. I know using append is slow but I cannot figure out an alternative. I tried to make it using tuples (with a slightly different configuration - no players and salary) but it ended up not working.
tuples = []
index = None
for year in nbaSalaryData.keys():
for team in nbaSalaryData[year]:
t = nbaSalaryData[year][team]
tuples.append((year, team))
index = pd.MultiIndex.from_tuples(tuples, names=["year", "team"])
df = index.to_frame()
df
Which outputs:
year team
year team
1990-1991 Cleveland 1990-1991 Cleveland
New York 1990-1991 New York
Detroit 1990-1991 Detroit
LA Lakers 1990-1991 LA Lakers
Atlanta 1990-1991 Atlanta
I'm not that familiar with pandas but realize there must be a faster way than append().
回答1:
You can adapt the answer to a very similar question as follow:
z = json.loads(json_data)
out = pd.Series({
(i,j,m): z[i][j][k][m]
for i in z
for j in z[i]
for k in ['players']
for m in z[i][j][k]
}).to_frame('salary').rename_axis('year team player'.split())
# out:
salary
year team player
1990-1991 Cleveland Hot Rod Williams $3,785,000
Danny Ferry $2,640,000
Mark Price $1,400,000
Brad Daugherty $1,320,000
Larry Nance $1,260,000
Chucky Brown $630,000
Steve Kerr $548,000
Derrick Chievous $525,000
Winston Bennett $525,000
John Morton $350,000
Milos Babic $200,000
Gerald Paddio $120,000
Darnell Valentine $100,000
Henry James $75,000
Also, if you intend to do some numerical analysis with those salaries, you probably want them as numbers, not strings. If so, also consider:
out['salary'] = pd.to_numeric(out['salary'].str.replace(r'\D', ''))
PS: Explanation:
The for lines are just one big comprehension to flatten your nested dict. To understand how it works, try first:
[
(i,j)
for i in z
for j in z[i]
]
The 3rd for would be to list all keys of z[i][j], which would be: ['salary', 'players', 'url'], but we are only interested in 'players', so we say so.
The final bit is, instead of a list, we want a dict. Try the expression without surrounding with pd.Series() and you'll see exactly what's going on.
回答2:
We can use the for loop to create the dataframe and append, before finally concatenating: Delaying the concatenation till the end is much better than appending dataframes within the loop
box = []
# data refers to the shared json in the question
for year, value in data.items():
for team, players in value.items():
content = players["players"]
content = pd.DataFrame.from_dict(
content, orient="index", columns=["salary"]
).rename_axis(index="player")
content = content.assign(year=year, team=team)
box.append(content)
box
[ salary year team
player
Hot Rod Williams $3,785,000 1990-1991 Cleveland
Danny Ferry $2,640,000 1990-1991 Cleveland
Mark Price $1,400,000 1990-1991 Cleveland
Brad Daugherty $1,320,000 1990-1991 Cleveland
Larry Nance $1,260,000 1990-1991 Cleveland
Chucky Brown $630,000 1990-1991 Cleveland
Steve Kerr $548,000 1990-1991 Cleveland
Derrick Chievous $525,000 1990-1991 Cleveland
Winston Bennett $525,000 1990-1991 Cleveland
John Morton $350,000 1990-1991 Cleveland
Milos Babic $200,000 1990-1991 Cleveland
Gerald Paddio $120,000 1990-1991 Cleveland
Darnell Valentine $100,000 1990-1991 Cleveland
Henry James $75,000 1990-1991 Cleveland]
Concatenate and reorder index levels:
(
pd.concat(box)
.set_index(["year", "team"], append=True)
.reorder_levels(["year", "team", "player"])
)
来源：https://stackoverflow.com/questions/65573305/faster-way-to-make-pandas-multiindex-dataframe-than-append