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adding left and right view to DataFrame, equivalent to head() and tail() #7005

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adding left and right view to DataFrame, equivalent to head() and tail() #7005

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61e102a
adding left and right view to DataFrame, equivalent to head() and tail()
Apr 29, 2014
f26cf9e
moving left() and right() helpers from core to frame and adding tests
Apr 30, 2014
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18 changes: 18 additions & 0 deletions pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1733,6 +1733,24 @@ def _getitem_frame(self, key):
raise ValueError('Must pass DataFrame with boolean values only')
return self.where(key)

def left(self, n=5):
"""
Return first n columns
"""
l = self.shape[1]
if l == 0 or n == 0:
return self
return self.iloc[:, :n]

def right(self, n=5):
"""
Return last n columns
"""
l = self.shape[1]
if l == 0 or n == 0:
return self
return self.iloc[:, -n:]

def query(self, expr, **kwargs):
"""Query the columns of a frame with a boolean expression.

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2 changes: 1 addition & 1 deletion pandas/core/generic.py
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Expand Up @@ -1781,7 +1781,7 @@ def head(self, n=5):
Returns first n rows
"""
l = len(self)
if l == 0 or n==0:
if l == 0 or n == 0:
return self
return self.iloc[:n]

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23 changes: 23 additions & 0 deletions pandas/tests/test_frame.py
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Expand Up @@ -4470,6 +4470,29 @@ def test_head_tail(self):
assert_frame_equal(empty_df.tail(), empty_df)
assert_frame_equal(empty_df.head(), empty_df)

def test_left_right(self):
assert_frame_equal(self.frame.left(), self.frame.iloc[:, :5])
assert_frame_equal(self.frame.right(), self.frame.iloc[:, -5:])
assert_frame_equal(self.frame.left(0), self.frame)
assert_frame_equal(self.frame.right(0), self.frame)
assert_frame_equal(self.frame.left(-1), self.frame.iloc[:, :-1])
assert_frame_equal(self.frame.right(-1), self.frame.iloc[:, 1:])
assert_frame_equal(self.frame.left(1), self.frame.iloc[:, :1])
assert_frame_equal(self.frame.right(1), self.frame.iloc[:, -1:])
# with a float index
df = self.frame.copy()
df.index = np.arange(len(self.frame)) + 0.1
assert_frame_equal(df.left(), df.iloc[:, :5])
assert_frame_equal(df.right(), df.iloc[:, -5:])
assert_frame_equal(df.left(0), df)
assert_frame_equal(df.right(0), df)
assert_frame_equal(df.left(-1), df.iloc[:, :-1])
assert_frame_equal(df.right(-1), df.iloc[:, 1:])
#test empty dataframe
empty_df = DataFrame()
assert_frame_equal(empty_df.right(), empty_df)
assert_frame_equal(empty_df.left(), empty_df)

def test_insert(self):
df = DataFrame(np.random.randn(5, 3), index=np.arange(5),
columns=['c', 'b', 'a'])
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