如何为每个循环遍历数据帧中的两列？

Question

I have a dataframe containing 7 columns and I want to simultaneously loop through two of them to compare the values in each row. This is my for loop header, where watchCol and diaryCol are column numbers:

for watch, diary in df.iloc[:, watchCol], df.iloc[:, diaryCol]:

When I run this, I get the following error on that line:

ValueError: too many values to unpack (expected 2)

What am I doing wrong?

Thanks

EDIT:

Both columns contain datetimes. I need to compare the two values, and if the difference is within a certain range, I copy the value from the watchCol into another column, otherwise I move to the next row.

Answer 1

If you're trying to compare entries row by row, try this:

import pandas as pd  
df = pd.DataFrame({"a": [2, 2, 2, 2, 2], "b": [4, 3, 2, 1, 0]})

df["a greater than b"] = df.apply(lambda x: x.a > x.b, axis=1)
print df

   a  b a greater than b
0  2  4            False
1  2  3            False
2  2  2            False
3  2  1             True
4  2  0             True

That said, if you did want to loop through the elements row by row:

for a, b in zip(df.iloc[:, 0], df.iloc[:, 1]):
    print a, b

2 4
2 3
2 2
2 1
2 0