将列表更改映射到他们的新索引 Python

Question

I am working on a piece of software that clusters images for the user to label. Each iteration the user can merge clusters or rename the label of the clusters and I am looking for an algorithm to map the previous cluster index to its new index based on the previous cluster list and the input cluster list. I am holding the previous cluster's labeled names in a previous_classes list. If the user marks 'Ignore', map new cluster to -1 and remove cluster. Below is the workflow with 4 edge-cases I am looking to account for:

Iteration 1:

Merging ClassC to ClassE

Input:

previous_clusters = ["ClassA", "ClassB", "ClassC", "ClassD", "ClassE"]
clusters = ["ClassA", "ClassB", "ClassE", "ClassD", "ClassE"]

desired output:

{0:0, 1:1, 2:2, 3:3, 4:2}

Iteration 2:

Merging classA to ClassE

Input:

previous_clusters = ["ClassA", "ClassB", "ClassE", "ClassD"]
clusters = ["ClassE", "ClassB", "ClassE", "ClassD"]

desired output:

{0:0, 1:1, 2:0, 3:2}

Iteration 3:

Renaming classB to ClassF gives

Input:

previous_clusters = ["ClassE", "ClassB", "ClassD"]
clusters = ["ClassE", "ClassF", "ClassD"]

desired output:

{0:0, 1:1, 2:2}

Iteration 4

Ignoring ClassE

Input:

previous_clusters = ["ClassE", "ClassF", "ClassD"]
clusters = ["Ignore", "ClassF", "ClassD"]

desired output:

{0:-1, 1:0, 2:1}

previous_clusters = ["ClassF", "ClassD"]

Answer 1

Note that you don't need previous_clusters (although it was helpful for me to understand the context). The only information you need is something like "as for index 0, the user selects 'ClassA' ". You can collect all indices that maps to 'ClassA' , and then invert the map (while giving unique indices to the new classes, and dealing with -1 ).

from collections import defaultdict

def recluster(new):
    indices_mapped_to = defaultdict(list)
    indices_ignored = [] # list of indices to be ignored

    for i, new_class in enumerate(new):
        if new_class == 'Ignore':
            indices_ignored.append(i)
        else:
            indices_mapped_to[new_class].append(i)

    # "invert" the dict
    output = {j: i for i, v in enumerate(indices_mapped_to.values()) for j in v}
    output.update({j: -1 for j in indices_ignored}) # add the ignored cases

    return output

print(recluster(["ClassA", "ClassB", "ClassE", "ClassD", "ClassE"]))
# {0: 0, 1: 1, 2: 2, 4: 2, 3: 3}
print(recluster(["ClassE", "ClassB", "ClassE", "ClassD"]))
# {0: 0, 2: 0, 1: 1, 3: 2}
print(recluster(["ClassE", "ClassF", "ClassD"]))
# {0: 0, 1: 1, 2: 2}
print(recluster(["Ignore", "ClassF", "ClassD"]))
# {1: 0, 2: 1, 0: -1}