how to make a null query selecting all the items

Question

I really like the query method. What is the null query that select all the items? I have tried df.query("True") , but it doesn't work.

The only thing I have found to work is df.query("index == 0 | index != 0") .

Why "True" is not working, it is a predicate.

Answer 1

For me works:

df.query("index")

Sample:

df = pd.DataFrame({'A':[1,2,3],
                   'B':[4,5,6]},
                   index=[-1,4,5])

print (df)
    A  B
-1  1  4
 4  2  5
 5  3  6

a = df.query("index")
print (a)
    A  B
-1  1  4
 4  2  5
 5  3  6

If index values are not negative, use:

a = df.query("index > -1")
print (a)
   A  B
0  1  4
1  2  5
2  3  6

EDIT by comment:

I am not query expert, but if use True only, it search values in index:

df = pd.DataFrame({'A':[1,2,3],
                   'B':[4,5,6]}, 
                    index=[True,0,'d'])

print (df)
      A  B
True  1  4
0     2  5
d     3  6

a = df.query("True")
print (a)
A    1
B    4
Name: True, dtype: int64

b = df.query('0')
print (b)
A    2
B    5
Name: 0, dtype: int64

Another crazy index:

df = pd.DataFrame({'A':[1,2,3],
                   'B':[4,5,6]}, 
                    index=[True,True,True])

print (df)
      A  B
True  1  4
True  2  5
True  3  6

a = df.query("True")
print (a)
      A  B
True  1  4
True  2  5
True  3  6