python - 我正在尝试访问数据框中的列并对其进行操作并在数据 fame 中创建新列

Question

x = onefile1['quiz1']
grading = []
for i in x :
    if i == '-':
        grading.append(0)

    elif float(i) < float(50.0):
        grading.append('lessthen50')

    elif i > 50.0 and i < 60.0:
        grading.append('between50to60')

    elif i > 60.0 and i < 70.0:
        grading.append('between60to70')


    elif i > 70.0 and i < 80.0:
        grading.append('between70to80')

    elif i  > 80.0:
        grading.append('morethen80')

    else:
        grading.append(0) 

onefile1 = file.reset_index()
onefile1['grade'] = grading

它给了我以下错误：

值的长度与索引的长度不匹配

Answer 1

您的值可能等于 50、60 或 70 等。您可以使用pandas<=来代替<或cut使用 pandas，

import numpy as np
import pandas as pd

onefile1['quiz1'] = (onefile1['quiz1']
                        .astype(str).str.replace('-', '0')
                        .astype(float))

labels = [
    0, 'lessthen50', 'between50to60', 
    'between60to70', 'between70to80', 'morethen80'
]

bins = [-1, 0, 50, 60, 70, 80, np.inf]
onefile1['grade'] = pd.cut(
    onefile1.quiz1, bins=bins, 
    labels=labels, include_lowest=True)

这是一个例子，

>>> import numpy as np
>>> import pandas as pd
>>> onefile1 = pd.DataFrame({'quiz1': [0, 40, 30, 60, 80, 100, '-']})
>>> onefile1['quiz1'] = (onefile1['quiz1']
                        .astype(str).str.replace('-', '0')
                        .astype(float))
>>> labels = [
    0, 'lessthen50', 'between50to60',
    'between60to70', 'between70to80', 'morethen80'
]
>>> bins = [-1, 0, 50, 60, 70, 80, np.inf]
>>> onefile1['grade'] = pd.cut(
    onefile1.quiz1, bins=bins,
    labels=labels, include_lowest=True)
>>> onefile1
   quiz1          grade
0    0.0              0
1   40.0     lessthen50
2   30.0     lessthen50
3   60.0  between50to60
4   80.0  between70to80
5  100.0     morethen80
6    0.0              0

PS：最好在使用前检查include_lowest参数right。