I am very new to pandas dataframes and I have a dataframe similar to this one:

value_1 value_2
1       2
9       6
2       5
7       2
2       5

What I need to do is to only get the rows that have a value_1 greater than 3 for example, but also get the first and last row of the dataframe. Like this:

value_1 value_2
1       2
9       6
7       2
2       5

I know that I can filter by index with iloc and by column value with loc, but how can I use them both together?

Thanks!

CodePudding user response：

Assuming a range index, you could use boolean indexing:

# is value_1 > 3?
m1 = df['value_1'].gt(3)
# is the index the first or last value?
m2 = df.index.isin([0, len(df)-1])
# keep if any condition above is True
out = df[m1|m2]

If you don't have a range index or if you have duplicates, you can use:

m2 = np.r_[True, [False]*len(df-2), True]

output:

   value_1  value_2
0        1        2
1        9        6
3        7        2
4        2        5