python - Determining when a column value changes in pandas dataframe

Question

I am looking to write a quick script that will run through a csv file with two columns and provide me the rows in which the values in column B switch from one value to another:

eg:

dataframe:

# |  A  |  B  
--+-----+-----
1 |  2  |  3
2 |  3  |  3
3 |  4  |  4
4 |  5  |  4
5 |  5  |  4

would tell me that the change happened between row 2 and row 3. I know how to get these values using for loops but I was hoping there was a more pythonic way of approaching this problem.

Answer 1

You can create a new column for the difference

> df['C'] = df['B'].diff()
> print df
   #  A  B   C
0  1  2  3 NaN
1  2  3  3   0
2  3  4  4   1
3  4  5  4   0
4  5  5  4   0

> df_filtered = df[df['C'] != 0]
> print df_filtered
   #  A  B  C
2  3  4  4  1

This will your required rows