python - 将一列数据附加到现有数据框

Question

我想将数据列表附加到数据框，以便该列表将出现在列中，即:

#Existing dataframe:
[A, 20150901, 20150902
 1  4  5
 4  2  7]

#list of data to append to column A:
data = [8,9,4]

#Required dataframe
[A, 20150901, 20150902
 1  4  5
 4  2  7
 8, 0  0
 9  0  0
 4  0  0]

我正在使用以下内容:

df_new = df.copy(deep=True)
#I am copying and deleting data as column names are type Timestamp and easier to reuse them
df_new.drop(df_new.index, inplace=True)
for item in data_list:
    df_new = df_new.append([{'A':item}], ignore_index=True)
df_new.fillna(0, inplace=True) 
df = pd.concat([df, df_new],  axis=0, ignore_index=True)   

但是在循环中执行此操作效率低下而且我收到此警告:

Passing list-likes to .loc or [] with any missing label will raise
KeyError in the future, you can use .reindex() as an alternative.

关于如何克服此错误并一次附加 2 个数据帧有什么想法吗？

Answer 1

我认为需要concat包含 A 列的新 DataFrame，然后是 reindex如果想要相同顺序的列并最后用 fillna 替换缺失值:

data = [8,9,4]
df_new = pd.DataFrame({'A':data})

df = (pd.concat([df, df_new], ignore_index=True)
        .reindex(columns=df.columns)
        .fillna(0, downcast='infer'))
print (df)
   A  20150901  20150902
0  1         4         5
1  4         2         7
2  8         0         0
3  9         0         0
4  4         0         0