How to delete the last row of data of a pandas dataframe

I think this should be simple, but I tried a few ideas and none of them worked:

last_row = len(DF)
DF = DF.drop(DF.index[last_row])  #<-- fail!

I tried using negative indices but that also lead to errors. I must still be misunderstanding something basic.

Solution 1:

To drop last n rows:

df.drop(df.tail(n).index,inplace=True) # drop last n rows

By the same vein, you can drop first n rows:

df.drop(df.head(n).index,inplace=True) # drop first n rows

Solution 2:

DF[:-n]

where n is the last number of rows to drop.

To drop the last row :

DF = DF[:-1]

Solution 3:

Since index positioning in Python is 0-based, there won't actually be an element in index at the location corresponding to len(DF). You need that to be last_row = len(DF) - 1:

In [49]: dfrm
Out[49]: 
          A         B         C
0  0.120064  0.785538  0.465853
1  0.431655  0.436866  0.640136
2  0.445904  0.311565  0.934073
3  0.981609  0.695210  0.911697
4  0.008632  0.629269  0.226454
5  0.577577  0.467475  0.510031
6  0.580909  0.232846  0.271254
7  0.696596  0.362825  0.556433
8  0.738912  0.932779  0.029723
9  0.834706  0.002989  0.333436

[10 rows x 3 columns]

In [50]: dfrm.drop(dfrm.index[len(dfrm)-1])
Out[50]: 
          A         B         C
0  0.120064  0.785538  0.465853
1  0.431655  0.436866  0.640136
2  0.445904  0.311565  0.934073
3  0.981609  0.695210  0.911697
4  0.008632  0.629269  0.226454
5  0.577577  0.467475  0.510031
6  0.580909  0.232846  0.271254
7  0.696596  0.362825  0.556433
8  0.738912  0.932779  0.029723

[9 rows x 3 columns]

However, it's much simpler to just write DF[:-1].

Solution 4:

Surprised nobody brought this one up:

# To remove last n rows
df.head(-n)

# To remove first n rows
df.tail(-n)

Running a speed test on a DataFrame of 1000 rows shows that slicing and head/tail are ~6 times faster than using drop:

>>> %timeit df[:-1]
125 µs ± 132 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

>>> %timeit df.head(-1)
129 µs ± 1.18 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

>>> %timeit df.drop(df.tail(1).index)
751 µs ± 20.4 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

Solution 5:

Just use indexing

df.iloc[:-1,:]

That's why iloc exists. You can also use head or tail.