如何重写此代码以列出理解

Question

I am trying to append string to each value in df. I'd like to improve speed of code (big df). I tried to rewrite code and use list comprehension, but I am stuck. Here is a snippet of my code:

beginning ='begin ' #word on the beginning of the column
c=list(df.columns) #list of all column in the dataframe

for i in c:
    df[i] = beginning + df[i].astype(str)

Can Someone Help Me, Please?

Answer 1

Just do string addition to dataframe.

Here's an example dataframe with multiple columns of different types.

In [823]: df
Out[823]:
   A  B          C    D
0  A  1 2010-03-31  1.0
1  B  2 2010-04-01  2.0
2  C  3 2010-04-02  3.0

Convert to str type and add string.

In [824]: 'begin ' + df.astype(str)
Out[824]:
         A        B                 C          D
0  begin A  begin 1  begin 2010-03-31  begin 1.0
1  begin B  begin 2  begin 2010-04-01  begin 2.0
2  begin C  begin 3  begin 2010-04-02  begin 3.0