Python Pandas-根据匹配条件创建新的df列

Question

I am attempting to create a new column in my pandas data frame(df). The value for each row in this column (call it column_new) needs to look at a reference column (column_ref) that already exists in the data frame. I used the unique values in column_ref and assigned them as keys in a dictionary, d:

d = {'column_ref_value1': 'a',
     'column_ref_value2': 'b', 
     'column_ref_value3': 'c',}

The values in dict(d) are values that I want to assign to to column_new in my data frame. Here is what I tried to no avail:

for i in df['column_ref']:
    for k, v in d.items(): 
        if k == i:
            df['column_new'] = v

When I call my df I am seeing column_new populated with value 'c' in every row, and I am not sure why. I'm guessing my issue has to do with improper iterating through a pandas dataframe or series.

Thanks in advance!

Answer 1

您可以使用replace（） ：

df['column_new'] = df.replace({'column_ref': d})