# Version 1.0.1¶

## Critical bug fix¶

We fixed a critical bug introduced in Koalas 1.0.0 (#1609).

If we call DataFrame.rename with columns parameter after some operations on the DataFrame, the operations will be lost:

>>> kdf = ks.DataFrame([[1, 2, 3, 4], [5, 6, 7, 8]], columns=["A", "B", "C", "D"])
>>> kdf1 = kdf + 1
>>> kdf1
A  B  C  D
0  2  3  4  5
1  6  7  8  9
>>> kdf1.rename(columns={"A": "aa", "B": "bb"})
aa  bb  C  D
0   1   2  3  4
1   5   6  7  8


This should be:

>>> pdf1.rename(columns={"A": "aa", "B": "bb"})
aa  bb  C  D
0   2   3  4  5
1   6   7  8  9


## Other improvements¶

• Clean up InternalFrame and around anchor. (#1601)

• Fixing DataFrame.iteritems to return generator (#1602)

• Clean up groupby to use the anchor. (#1610)