pandas python how to count the number of records or rows in a dataframe

To get the number of rows in a dataframe use:

df.shape[0]

(and df.shape[1] to get the number of columns).

As an alternative you can use

len(df)

or

len(df.index)

(and len(df.columns) for the columns)

shape is more versatile and more convenient than len(), especially for interactive work (just needs to be added at the end), but len is a bit faster (see also this answer).

To avoid: count() because it returns the number of non-NA/null observations over requested axis

len(df.index) is faster

import pandas as pd
import numpy as np

df = pd.DataFrame(np.arange(24).reshape(8, 3),columns=['A', 'B', 'C'])
df['A'][5]=np.nan
df
# Out:
#     A   B   C
# 0   0   1   2
# 1   3   4   5
# 2   6   7   8
# 3   9  10  11
# 4  12  13  14
# 5 NaN  16  17
# 6  18  19  20
# 7  21  22  23

%timeit df.shape[0]
# 100000 loops, best of 3: 4.22 µs per loop

%timeit len(df)
# 100000 loops, best of 3: 2.26 µs per loop

%timeit len(df.index)
# 1000000 loops, best of 3: 1.46 µs per loop

df.__len__ is just a call to len(df.index)

import inspect 
print(inspect.getsource(pd.DataFrame.__len__))
# Out:
#     def __len__(self):
#         """Returns length of info axis, but here we use the index """
#         return len(self.index)

Why you should not use count()

df.count()
# Out:
# A    7
# B    8
# C    8

Regards to your question... counting one Field? I decided to make it a question, but I hope it helps...

Say I have the following DataFrame

import numpy as np
import pandas as pd

df = pd.DataFrame(np.random.normal(0, 1, (5, 2)), columns=["A", "B"])

You could count a single column by

df.A.count()
#or
df['A'].count()

both evaluate to 5.

The cool thing (or one of many w.r.t. pandas) is that if you have NA values, count takes that into consideration.

So if I did

df['A'][1::2] = np.NAN
df.count()

The result would be

 A    3
 B    5

Simply, row_num = df.shape[0] # gives number of rows, here's the example:

import pandas as pd
import numpy as np

In [322]: df = pd.DataFrame(np.random.randn(5,2), columns=["col_1", "col_2"])

In [323]: df
Out[323]: 
      col_1     col_2
0 -0.894268  1.309041
1 -0.120667 -0.241292
2  0.076168 -1.071099
3  1.387217  0.622877
4 -0.488452  0.317882

In [324]: df.shape
Out[324]: (5, 2)

In [325]: df.shape[0]   ## Gives no. of rows/records
Out[325]: 5

In [326]: df.shape[1]   ## Gives no. of columns
Out[326]: 2