CODEWITHSUNDEEP
pythonpandas
viva
viva

Reputation: 103

Pandas dataframe query() throws error when dataframe size is more than 100 rows

Code snippet 1 

import pandas as pd  
df = pd.read_csv("filename.txt", sep='\t', header = 0, names = ['E', 'S', 'D'])  
Result = df.query(df.E.head(**n=100**) == 0)

Code Snippet 1 works as expected and returns a dataframe with df.E value equal to 0. But,

Code Snippet 2 

import pandas as pd  
df = pd.read_csv("filename.txt", sep='\t', header = 0, names = ['E', 'S', 'D'])  
Result = df.query(df.E.head(**n=101**) == 0)

Code Snippet 2 does not work and throws error as 

"SyntaxError: ('invalid syntax', ('<unknown>', 1, 602, '[True ,True
,True ,True ,True ,True ,True ,True ,True ,True ,True ,True ,True
,True ,True ,True ,... ,True ,True ,True ,True ,True ,True ,True ,True
,True ,True ,True ,True ,True ,True ,True ,...]\n'))"

Please note that only change between 2 sets of code is n=100 and n=101.

The error is still present with .head(n=101) removed. Have tried for many values greater than 100, throws same error.

Upvotes: 1

Views: 3826

Answers (1)

Jeff
Jeff

Reputation: 129018

df.query accepts a string query. you are not passing valid python (it accepts a slight superset of python actually). so I wouldn't expect either of your code snippets to work at all, hence the SyntaxError.

Straight out of the doc-string

Parameters
----------
expr : string
    The query string to evaluate.  You can refer to variables
    in the environment by prefixing them with an '@' character like
    ``@a + b``.


In [14]: pd.set_option('max_rows',10)

In [15]: np.random.seed(1234)

In [16]: df = DataFrame(np.random.randint(0,10,size=100).reshape(-1,1),columns=list('a'))

In [17]: df
Out[17]: 
    a
0   3
1   6
2   5
3   4
4   8
.. ..
95  9
96  2
97  9
98  1
99  3

[100 rows x 1 columns]

In [18]: df.query('a==3')
Out[18]: 
    a
0   3
21  3
26  3
28  3
30  3
32  3
51  3
60  3
99  3

In [19]: var = 3

In [20]: df.query('a==@var')
Out[20]: 
    a
0   3
21  3
26  3
28  3
30  3
32  3
51  3
60  3
99  3

Upvotes: 1

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