从另一列 pandas df 分配值的有效方法

Question

我正在尝试创建一个更高效的脚本，该脚本根据另一列中的值创建一个新的column。下面的脚本执行此操作，但我一次只能选择一个string。我想对所有单个值执行此操作。

对于下面的df，我目前正在对Location 中的每个string 运行脚本。但是，我想在所有uniquestrings 上运行脚本。

关于如何分配新列的说明：Location 中的每个 string 获取 Day 中前 3 个唯一项的值。因此，对于Location 中的每个值，都会为Day 中的前三个唯一值分配一个新字符串。

import pandas as pd
import numpy as np

d = ({
    'Day' : ['Mon','Tues','Wed','Wed','Thurs','Thurs','Fri','Mon','Sat','Fri','Sun'],                 
    'Location' : ['Home','Home','Away','Home','Away','Home','Home','Home','Home','Away','Home'],        
    })

df = pd.DataFrame(data=d)

#Select value
mask = df['Location'] == 'Home'
df1 = df[mask].drop_duplicates('Day')
d = dict(zip(df1['Day'], np.arange(len(df1)) // 3 + 1))

df.loc[mask, 'Assign'] = df.loc[mask, 'Day'].map(d)

目前我正在选择['Location'] 中的每个值，例如mask = df['Location'] == 'Home'。

我想在所有价值观上都这样做。例如mask = df['Location'] == All unique values

预期输出：

      Day Location Assign
0     Mon     Home     C1
1    Tues     Home     C1
2     Wed     Away     C2
3     Wed     Home     C1
4   Thurs     Away     C2
5   Thurs     Home     C3
6     Fri     Home     C3
7     Mon     Home     C1
8     Sat     Home     C3
9     Fri     Away     C2
10    Sun     Home     C4

Answer 1

你可以使用：

def f(x):
    #get unique days
    u = x['Day'].unique()
    #mapping dictionary
    d = dict(zip(u, np.arange(len(u)) // 3 + 1))
    x['new'] = x['Day'].map(d)
    return x

df = df.groupby('Location', sort=False).apply(f)
#add Location column
s = df['new'].astype(str) + df['Location']
#encoding by factorize
df['new'] = pd.Series(pd.factorize(s)[0] + 1).map(str).radd('C')
print (df)
      Day Location new
0     Mon     Home  C1
1    Tues     Home  C1
2     Wed     Away  C2
3     Wed     Home  C1
4   Thurs     Away  C2
5   Thurs     Home  C3
6     Fri     Home  C3
7     Mon     Home  C1
8     Sat     Home  C3
9     Fri     Away  C2
10    Sun     Home  C4

Answer 2

# DataFrame Given
df = pd.DataFrame({
    'Day' : ['Mon','Tues','Mon','Wed','Thurs','Fri','Mon','Sat','Sun','Tues'],                 
    'Location' : ['Home','Home','Away','Home','Home','Home','Home','Home','Home','Away'],                   
     })
Unique_group = ['Mon','Tues','Wed']
df['Group'] = df['Day'].apply(lambda x:1 if x in Unique_group else 2)
df['Assign'] = np.zeros(len(df))
# Assigning the ditionary values for output from numeric
vals = dict([(i,'C'+str(i)) for i in range(len(df))])

循环剪切每一行的数据框并检查前一个“分配”列信息以分配新值

for i in range(1,len(df)+1,1):
    # Slicing the Dataframe line by line
    df1 = df[:i]
    # Incorporating the conditions of Group and Location
    df1 = df1[(df1.Location == df1.Location.loc[i-1]) & (df1.Group == df1.Group.loc[i-1]) ]
    # Writing the 'Assign' value for the first line of sliced df
    if len(df1)==1:
        df.loc[i-1,'Assign'] = df[:i].Assign.max()+1
    # Writing the 'Assign value based on previous values if it has contiuos 2 values of same group
    elif (df1.Assign.value_counts()[df1.Assign.max()] <3):
        df.loc[i-1,'Assign'] = df1.Assign.max()
    # Writing 'Assign' value for new group
    else:
        df.loc[i-1,'Assign'] = df[:i]['Assign'].max()+1
df.Assign = df.Assign.map(vals)

输出：

     Day    Location    Group   Assign
0   Mon Home    1   C1
1   Tues    Home    1   C1
2   Mon Away    1   C2
3   Wed Home    1   C1
4   Thurs   Home    2   C3
5   Fri Home    2   C3
6   Mon Home    1   C4
7   Sat Home    2   C3
8   Sun Home    2   C5
9   Tues    Away    1   C2

Answer 3

在第二次尝试时有效。

这个问题很难理解。

我确信这应该用 pandas 来完成 groupby() 和数据框合并，如果你检查 这个回复的历史你可以看到我是如何 更改了答案以替换更慢的 Python 带有快速 Pandas 代码的代码。

下面的代码首先计算每个唯一值 位置，然后使用辅助数据框 创造最终价值。

我建议将此代码粘贴到 Jupyter 笔记本中 并检查中间步骤。

import pandas as pd
import numpy as np

d = ({
    'Day' : ['Mon','Tues','Wed','Wed','Thurs','Thurs','Fri','Mon','Sat','Fri','Sun'],                 
    'Location' : ['Home','Home','Away','Home','Away','Home','Home','Home','Home','Away','Home'],        
    })

df = pd.DataFrame(data=d)

# including the example result
df["example"] = pd.Series(["C" + str(e) for e in [1, 1, 2, 1, 2, 3, 3, 1, 3, 2, 4]])

# this groups days per location
s_grouped = df.groupby(["Location"])["Day"].unique()

# This is the 3 unique indicator per location
df["Pre-Assign"] = df.apply(
    lambda x: 1 + list(s_grouped[x["Location"]]).index(x["Day"]) // 3, axis=1
)

# Now we want these unique per combination
df_pre = df[["Location", "Pre-Assign"]].drop_duplicates().reset_index().drop("index", 1)
df_pre["Assign"] = 'C' + (df_pre.index + 1).astype(str)

# result
df.merge(df_pre, on=["Location", "Pre-Assign"], how="left")

结果

其他数据帧/系列：

Answer 4

没有那么漂亮，但比 groupby/apply 方法快得多......

def get_ordered_unique(a):
    u, idx = np.unique(a, return_index=True)
    # get ordered unique values
    return a[np.sort(idx)]

# split ordered unique value array into arrays of size 3
def find_ugrps(a):
    ord_u = get_ordered_unique(a)

    if ord_u.size > 3:
        split_idxs = [i for i in range(1, ord_u.size) if i % 3 == 0]
        u_grps = np.split(ord_u, split_idxs)
    else:
        u_grps = [ord_u]

    return u_grps

locs = pd.factorize(df.Location)[0] + 1
days = pd.factorize(df.Day)[0] + 1

assign = np.zeros(days.size).astype(int)
unique_locs = get_ordered_unique(locs)

i = 0
for loc in unique_locs:
    i += 1
    loc_idxs = np.where(locs == loc)[0]
    # find the ordered unique day values for each loc val slice
    these_unique_days = get_ordered_unique(days[loc_idxs])
    # split into ordered groups of three
    these_3day_grps = find_ugrps(these_unique_days)
    # assign integer for days found within each group
    for ugrp in these_3day_grps:
        day_idxs = np.where(np.isin(days[loc_idxs], ugrp))[0]
        np.put(assign, loc_idxs[day_idxs], i)
        i += 1

# set proper ordering within assign array using factorize
df['Assign'] = (pd.factorize(assign)[0] + 1)
df['Assign'] = 'C' + df['Assign'].astype(str)

print(df)

      Day Location Assign
0     Mon     Home     C1
1    Tues     Home     C1
2     Wed     Away     C2
3     Wed     Home     C1
4   Thurs     Away     C2
5   Thurs     Home     C3
6     Fri     Home     C3
7     Mon     Home     C1
8     Sat     Home     C3
9     Fri     Away     C2
10    Sun     Home     C4