How to merge repeated elements in list in python?

Question

I have a list of coordinate like:

list_coordinate =[(9,0),(9,1),(9,3) ... (53,0),(53,1),(53,3)...(54,0),(54,1)..]

value = []

 for m in range(0,len(list_coordinate)):    
    if m != len(list_coordinate)-1:
        if list_coordinate[m][0]==list_coordinate[m+1][0]:
            value.append(list_coordinate[m][0])`

Output of this code:

value = [9,9 ,9,...,53,53,53,...,54,54,54,54...]

I want to merge this value list for similar element and want output as:

Expected output:

 [9,53,54]

Answer 1

you can use itertools.groupby

from itertools import groupby
value = [9,9 ,9,53,53,53,54,54,54,54]
g = [k for k,_ in groupby(value)]
print(g)

which produces

[9, 53, 54]

and it is guaranteed to be in the same order as the input list (if it matters).

Basically

groupby(iterable[, keyfunc])

groups the elements in the iterable, passing to a new group when the key function changes.

If the key function is omitted, the identity function is assumed, and the key for the group will be each element encountered.

So as long as the elements in value stay the same, they will be grouped under the same key, which is the element itself.

Note: this works for contiguous repetitions only. In case you wanted to get rid of re-occurring duplicates, you should sort the list first (as groupby docs explains)

As per your comment below, in case you wanted to operate on the coordinates directly

list_coordinate = [(9,0), (9,1), (9,3), (53,0), (53,1), (53,3), (54,0), (54,1)]
g = [k for k,_ in groupby(list_coordinate, lambda x: x[0])]
print(g)

produces the same output

[9, 53, 54]