如何将 Pandas Dataframe 中的最后 4 位数字替换为 0101，如果它们是 9999 (Python)

Question

我有一个如下所示的数据框：

OrdNo  year
1     20059999
2     20070830
3     20070719
4     20030719
5     20039999
6     20070911
7     20050918
8     20070816
9     20069999

如果 Pandas Dataframe 中的最后 4 位数字是 9999，如何用 0101 替换它们？

谢谢

Answer 1

假设您的

year

列的类型为

str

：

df["year"] = df["year"].str.replace("(9999)$", "0101")

如果是

numeric

类型

df["year"] = pd.to_numeric(df["year"].astype(str).str.replace("(9999)$", "0101"), errors="coerce")

Answer 2

我创建了一个脚本来解释如何解决这个问题。请注意，这是一个非常冗长的版本，它可能而且应该被压缩，但我已尽力使其尽可能清晰地遵循。 另外，如果您是新手开发人员，一个好的练习方法是想出一些步骤来解决您头脑中的问题（或写下来），并深入研究库的文档以尝试找到一个好的解决方案。

import pandas as pd

# Creating dataframe
data = [[1, 20059999], [2, 20070830], [3, 20070719], [4, 20030719], [5, 20039999], [6, 20070911], [7, 20050918], [8, 20070816], [9, 20069999]]
df = pd.DataFrame(data, columns=['OrdNo', 'year'])

# Iterating through dataframe
for index, row in df.iterrows():
    # Here we take the columns from the row we are in right now
    OrdNo = row['OrdNo']
    year = row['year']

    # Taking last four digits from year int. We need to convert the year int to string to do this. -4: basically
    # tells the code to start at the end (-), move 4 characters back (4) and return everything from that point to the
    # end (:)
    lastfour = str(year)[-4:]

    # Check if last four digits are 9999 (as string, because lastfour is a string)
    if lastfour == "9999":
        # If true, replace the 9999 with 0101
        # First we take the year but remove the last four digits (the 9999)
        year = str(year)[:-4]

        # Then we add 0101 to the year
        newyear = year + "0101"

        # Now convert it back to int
        newyear = int(newyear)

        # And put it back in the dataframe
        # We use loc to find based on the OrdNo and then we replace the year column by our new value
        df.loc[df['OrdNo'] == OrdNo, 'year'] = newyear

# Lets print the result
print(df.to_string(index=False))