merge in python

1new_df = pd.merge(A_df, B_df,  how='left', left_on=['A_c1','c2'], right_on = ['B_c1','c2'])

1def merge_sort(arr):
2    # The last array split
3    if len(arr) <= 1:
4        return arr
5    mid = len(arr) // 2
6    # Perform merge_sort recursively on both halves
7    left, right = merge_sort(arr[:mid]), merge_sort(arr[mid:])
8
9    # Merge each side together
10    return merge(left, right, arr.copy())
11
12
13def merge(left, right, merged):
14
15    left_cursor, right_cursor = 0, 0
16    while left_cursor < len(left) and right_cursor < len(right):
17      
18        # Sort each one and place into the result
19        if left[left_cursor] <= right[right_cursor]:
20            merged[left_cursor+right_cursor]=left[left_cursor]
21            left_cursor += 1
22        else:
23            merged[left_cursor + right_cursor] = right[right_cursor]
24            right_cursor += 1
25            
26    for left_cursor in range(left_cursor, len(left)):
27        merged[left_cursor + right_cursor] = left[left_cursor]
28        
29    for right_cursor in range(right_cursor, len(right)):
30        merged[left_cursor + right_cursor] = right[right_cursor]
31
32    return merged

1# df1 as main df and use the feild from df2 and map it into df1
2
3df1.merge(df2,on='columnName',how='left')

1import pandas as pd
2df1 = pd.DataFrame({'lkey': ['foo', 'bar', 'baz', 'foo'],
3                    'value': [1, 2, 3, 5]})
4df2 = pd.DataFrame({'rkey': ['foo', 'bar', 'baz', 'foo'],
5                    'value': [5, 6, 7, 8]})
6df1.merge(df2, left_on='lkey', right_on='rkey')

1>>> df1.merge(df2, left_on='lkey', right_on='rkey')
2  lkey  value_x rkey  value_y
30  foo        1  foo        5
41  foo        1  foo        8
52  foo        5  foo        5
63  foo        5  foo        8
74  bar        2  bar        6
85  baz        3  baz        7
9

1def merge(array, left_index, right_index, middle):
2    # Make copies of both arrays we're trying to merge
3
4    # The second parameter is non-inclusive, so we have to increase by 1
5    left_copy = array[left_index:middle + 1]
6    right_copy = array[middle+1:right_index+1]
7
8    # Initial values for variables that we use to keep
9    # track of where we are in each array
10    left_copy_index = 0
11    right_copy_index = 0
12    sorted_index = left_index
13
14    # Go through both copies until we run out of elements in one
15    while left_copy_index < len(left_copy) and right_copy_index < len(right_copy):
16
17        # If our left_copy has the smaller element, put it in the sorted
18        # part and then move forward in left_copy (by increasing the pointer)
19        if left_copy[left_copy_index] <= right_copy[right_copy_index]:
20            array[sorted_index] = left_copy[left_copy_index]
21            left_copy_index = left_copy_index + 1
22        # Opposite from above
23        else:
24            array[sorted_index] = right_copy[right_copy_index]
25            right_copy_index = right_copy_index + 1
26
27        # Regardless of where we got our element from
28        # move forward in the sorted part
29        sorted_index = sorted_index + 1
30
31    # We ran out of elements either in left_copy or right_copy
32    # so we will go through the remaining elements and add them
33    while left_copy_index < len(left_copy):
34        array[sorted_index] = left_copy[left_copy_index]
35        left_copy_index = left_copy_index + 1
36        sorted_index = sorted_index + 1
37
38    while right_copy_index < len(right_copy):
39        array[sorted_index] = right_copy[right_copy_index]
40        right_copy_index = right_copy_index + 1
41        sorted_index = sorted_index + 1
42