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

# This IPython notebook illustrates how to read the CSV files from disk as tables and set their metadata.

# First, we need to import *py_entitymatching* package and other libraries as follows:
# 

# In[1]:


import py_entitymatching as em
import pandas as pd
import os, sys


# ## Get the Path of the CSV File

#  the paths of the CSV file in the disk. For the convenience of the user, we have included some sample files in the package. The path of a sample CSV file can be obtained like this:

# In[2]:


# Get the datasets directory
datasets_dir = em.get_install_path() + os.sep + 'datasets'

# Get the paths of the input tables
path_A = datasets_dir + os.sep + 'person_table_A.csv'


# In[3]:


# Display the contents of the file in path_A
get_ipython().system('cat $path_A | head -3')


# ## Ways to Read a CSV File and Set Metadata

# There are three different ways to read a CSV file and set  metadata:
# 
# 1. Read a CSV file first, and then set the metadata
# 2. Read a CSV file and set the metadata together
# 3. Read a CSV file and set the metadata from a file in disk 

# ### Read the CSV file First and Then Set the Metadata

# First, read the CSV files as follows:

# In[4]:


A = em.read_csv_metadata(path_A)


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A.head()


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# Display the 'type' of A 
type(A)


# Then set the metadata for the table. We see `ID` is the key attribute (since it contains unique values and no value is missing) for the table. We can set this metadata as follows:

# In[7]:


em.set_key(A, 'ID')


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# Get the metadata that were set for table A
em.get_key(A)


# Now the CSV file is read into the memory and the metadata (i.e. key) is set for the table. 

# ### Read a CSV File and Set Metadata Together

# In the above, we saw that we first read in the CSV file and then set the metadata. These two steps can be combined into a single step like this:

# In[9]:


A = em.read_csv_metadata(path_A, key='ID')


# In[10]:


# Display the 'type' of A
type(A)


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# Get the metadata that were set for the table A 
em.get_key(A)


# ### Read a CSV File and Set Metadata from a File in Disk

# The user can specify the metadata in a file.
# 
# This file *MUST* be in the same directory as the CSV file and the file name 
# should be same, except the extension is set to '.metadata'.

# In[12]:


# We set the metadata for table A (stored in person_table_A.CSV).

# Get the path where the metadata file must be stored
metadata_file = datasets_dir + os.sep + 'person_table_A.metadata'

# Specify the metadata for table A . Here we specify that 'ID' is the key attribute for the table. Note that this step 
# requires write permission to the datasets directory.
get_ipython().system("echo '#key=ID' > $metadata_file")


# In[13]:


# Read the CSV file for table A
A = em.read_csv_metadata(path_A)


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em.get_key(A)


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get_ipython().system('rm $metadata_file')