timsaucer commented on code in PR #915:
URL: https://github.com/apache/datafusion-python/pull/915#discussion_r1798327582
##########
python/datafusion/dataframe.py:
##########
@@ -223,6 +223,30 @@ def limit(self, count: int, offset: int = 0) -> DataFrame:
"""
return DataFrame(self.df.limit(count, offset))
+ def head(self, n: int) -> DataFrame:
Review Comment:
Would it be helpful to have a default `n`?
##########
python/datafusion/dataframe.py:
##########
@@ -223,6 +223,30 @@ def limit(self, count: int, offset: int = 0) -> DataFrame:
"""
return DataFrame(self.df.limit(count, offset))
+ def head(self, n: int) -> DataFrame:
+ """Return a new :py:class:`DataFrame` with a limited number of rows.
+
+ Args:
+ n: Number of rows to take from the head of the DataFrame.
+
+ Returns:
+ DataFrame after limiting.
+ """
+ return DataFrame(self.df.limit(n, 0))
+
+ def tail(self, n: int) -> DataFrame:
+ """Return a new :py:class:`DataFrame` with a limited number of rows.
+
+ Be aware this could be potentially expensive due to the size of the
frame.
+
Review Comment:
Is there a better way we could do this? Maybe add something upstream if
necessary?
As I'm thinking of it, I don't know that this operation is necessarily well
defined. Just like with `limit` when you call it multiple times on a large
dataframe you get different results, I would expect different results from
multiple calls here.
If we do put this in, I would suggest adding more text to the description to
explain why this is an expensive operation - that it performs a collect to
determine the size of the dataframe.
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