#!/usr/bin/env python
# coding: utf-8

# In[2]:


import pandas as pd
import numpy as np


# In[16]:


df = pd.DataFrame({'i':range(20),
                   'L':[chr(97+i) for i in range(20)]
                  })

df['L2'] = df['L']


# In[17]:


df.T


# In[20]:


n_rows=len(df)
n_shuffle=int(n_rows*0.4)
n_rows, n_shuffle


# In[12]:


pick_rows=np.random.permutation(list(range(n_rows)))[0:n_shuffle]
pick_rows


# In[13]:


shuffled_values=np.random.permutation(df['L2'][pick_rows])
shuffled_values


# In[14]:


df['L2'][pick_rows]=shuffled_values


# In[15]:


df.T