Question

我的数据框看起来像这样

plant ancestor1 ancestor2 ancestor3 ancestor4 ancestor5
XX     XX1          XX2      XX3      XX4       XX5
YY     YY1          YY2      YY3      YY4
ZY     ZZ1          ZZ2      YY2      YY3       YY4
SS1    SS2          SS3

对于每一种植物，我都希望拥有最古老的祖先。最终输出应该看起来像这样

plant oldest
XX     XX5
XX1    XX5
XX2    XX5
XX3    XX5
XX4    XX5
YY     YY4
YY1    YY4
YY2    YY4
YY3    YY4
ZY     YY4
ZZ1    YY4
ZZ2    YY4
SS1    SS3
SS2    SS3

我该如何实现？

Answer 1

df2 = df.ffill(axis=1).melt(id_vars='ancestor5', value_name='plant')
df2 = df2.rename(columns={'ancestor5': 'oldest'}).drop(columns='variable')
df2 = df2[df2['oldest'] != df2['plant']]
print(df2)

   oldest plant
0     XX5    XX
1     YY4    YY
2     YY4    ZY
3     SS3   SS1
4     XX5   XX1
5     YY4   YY1
6     YY4   ZZ1
7     SS3   SS2
8     XX5   XX2
9     YY4   YY2
10    YY4   ZZ2
12    XX5   XX3
13    YY4   YY3
14    YY4   YY2
16    XX5   XX4
18    YY4   YY3

说明：使用melt转换为长格式的数据框，但在执行此操作之前，请确保使用ffill确保有一列始终包含祖先。稍后，删除通过正向填充重复值的行。

Answer 2

这是一种使用numpy isin，重复和串联以及列表推导的快速方法。这种方式还允许空祖先位置为空字符串，无或任何其他占位符。

df_vals = df.values
# count the number of sub-ancestors in each row
repeats = (~np.isin(df_vals, ['', None])).sum(axis=1) - 1
# find the oldest ancestor in each row
oldest_ancestors = np.array([df_vals[row, col] for row, col in enumerate(repeats)])
# make the oldest column by repeating the each oldest ancestor for each sub-ancestor
oldest = np.repeat(oldest_ancestors, repeats)
# make the plant column by getting all the sub-ancestors from each row and concatenating
plant = np.concatenate([df_vals[row][:col] for row, col in enumerate(repeats)])
df2 = pd.DataFrame({'plant': plant, 'oldest': oldest})

-

print(df2)

   plant oldest
0     XX    XX5
1    XX1    XX5
2    XX2    XX5
3    XX3    XX5
4    XX4    XX5
5     YY    YY4
6    YY1    YY4
7    YY2    YY4
8    YY3    YY4
9     ZY    YY4
10   ZZ1    YY4
11   ZZ2    YY4
12   YY2    YY4
13   YY3    YY4
14   SS1    SS3
15   SS2    SS3

设置数据框：

df = pd.DataFrame({'plant': ['XX', 'YY', 'ZY', 'SS1'],
                   'ancestor1': ['XX1', 'YY1', 'ZZ1', 'SS2'],
                   'ancestor2': ['XX2', 'YY2', 'ZZ2', 'SS3'],
                   'ancestor3': ['XX3', 'YY3', 'YY2', None],
                   'ancestor4': ['XX4', 'YY4', 'YY3', None],
                   'ancestor5': ['XX5', None, 'YY4', None]})

Answer 3

也许这是

df = pd.DataFrame({'plant': ['x', 'y','z'], 
                   'ancestor1':['X1','Y1','Z2'],
                   'ancestor2':['X2','','Z2'],
                   'ancestor3':['X3','','']})
df['oldest'] = [list(filter(len,list(df.iloc[i])))[-1] for i in range(len(df))]

Answer 4

这是使用列表理解的另一种方法（也许有点难看）。

dfout = pd.DataFrame([
        (y, x[-1]) for x in [[i for i in ii if i] for ii in df.values] 
        for y in x[:-1]
    ], columns = ['plant', 'oldest']
)

完整示例：

import pandas as pd

df = pd.DataFrame({
    'plant': ['XX','YY','ZY'],
    'ancestor1': ['XX1','YY1','ZZ1'],
    'ancestor2': ['XX2','YY2',''],
    'ancestor3': ['XX3','','']
})

df = df[['plant','ancestor1','ancestor2','ancestor3']]
dfout = pd.DataFrame([
        (y, x[-1]) for x in [[i for i in ii if i] for ii in df.values] 
        for y in x[:-1]
    ], columns = ['plant', 'oldest']
)
print(dfout)

返回：

  plant oldest
0    XX    XX3
1   XX1    XX3
2   XX2    XX3
3    YY    YY2
4   YY1    YY2
5    ZY    ZZ1

在熊猫的继承树中找到第一个祖先

4 个答案: