How do I insert a one column Series into a single dataframe column in python?

Question

I took out and copied a column from a dataframe. Easy. I modified it and now I need to put it back in but I don't know how. I have tried countless methods and none of them work. Any help greatly appreciated.

Here's the code: [code]

for col in ["Shares__Basic_"]:
    tmp_col = data[col]
    count = 0
    index_no = data.columns.get_loc(col)
    while 1:
        result = sm.tsa.stattools.adfuller(tmp_col, autolag='AIC')
        pvalue = result[1]
        if pvalue > 0.01:
            tmp_col = tmp_col.diff()
            count = count + 1
            tmp_col = tmp_col.drop(tmp_col.index[0])
            print(col+" diffed")
        elif pvalue < 0.01:
            break
    while count > 0:
        tmp_col = pd.concat([pd.Series([float("nan")]), tmp_col])
        count = count - 1
    del data[col]
    data.insert(index_no, col, value=tmp_col)

[/code]

Answer 1

Try this to add the column over the existing column -

df = pd.DataFrame({'A':[1,2,3],'B':[4,5,6]}) #DUMMY DATASET
print(df)

#>>    A  B
#>> 0  1  4
#>> 1  2  5
#>> 2  3  6

modified_column = df['A']**2

#Adding it back over the existing columns
df['A'] = modified_column
print(df)

#>>    A  B
#>> 0  1  4
#>> 1  4  5
#>> 2  9  6

If you want to add it as an addition column, then try this -

#Adding it back as a new column
df['New_A'] = modified_column
print(df)

#>>    A  B  New_A
#>> 0  1  4      1
#>> 1  2  5      4
#>> 2  3  6      9

---

EDIT: ValueError: cannot reindex from a duplicate axis usually occurs when you have duplicate index values. You maybe corrupting the modified_column's index accidently. Reset it by using the original dataframe's index.

modified_column.index = df.index