Python. How can I output each instance of a for loop as a nested list, lists inside a list

Question

I have a code that checks if the number in the range is even or odd and performs an operation on them respectively. It appends the results of the operation into a list. However, I am trying to append each instance of the for loop as a separate list within a list. How can I modify my code to do this?


series = []
for i in range(13, -0, -1):
    while i > 1:
        if i % 2 == 0:
            i = i//2
            series.append(i)
        else:
            i = i*3+1
            series.append(i)
print(series)

azro · Accepted Answer · 2020-05-03 21:15:28Z

1

You need to define the inner list just after the for to get a fresh one at each iterate, then save it in series

series = []
for i in range(13, -0, -1):
    inner = []
    while i > 1:
        if i % 2 == 0:
            i = i // 2
            inner.append(i)
        else:
            i = i * 3 + 1
            inner.append(i)
    series.append(inner)

[[40, 20, ...], [6, 3,...], ...]

You might want to keep the correspondance with the value that led to this list, using a dict like

series = {}
for i in range(13, -0, -1):
    keep_i = i
    inner = []
    while i > 1:
        if i % 2 == 0:
            i = i // 2
            inner.append(i)
        else:
            i = i * 3 + 1
            inner.append(i)
    series[keep_i] = list(inner)

{13: [40, 20,...], 12: [6, 3,...],...}

answered May 3, 2020 at 21:15

azro

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2 Comments

Achuth Varghese Over a year ago

The result would be inner list in series list/dictionary. There will be only one item "inner list" in "series list/dictionary" since whatever the condition maybe "i" is appended to "inner list". maybe there should be two lists. Not sure.

azro Over a year ago

@AchuthVarghese From the reading "each instance of the for loop as a separate list" so each run should go in a separate list, that's doesn't talk about the if/else, just each run of the for is in a list

pintert3 · Accepted Answer · 2020-05-03 21:22:10Z

0

You can simply add the [] over each i like so: series.append([i]):

series = []
for i in range(13, -0, -1):
    while i > 1:
        if i % 2 == 0:
            i = i//2
            series.append([i])
        else:
            i = i*3+1
            series.append([i])
print(series)

answered May 3, 2020 at 21:22

pintert3

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1 Comment

Abramo Over a year ago

Thank you, but your example is for while loop, i need it for "for" loop. Azro got it right. Please keep contributing and welcome!

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