Unexpected pandas index error when using a for loop

Question

I have a Pandas DataFrame with the shape - (133, 6) - and I am trying to use iloc to iterate down the frame then select and append chunks of data to a list.

I have a list of start positions:

start_positions = [6, 32, 58, 84, 110]

and the end positions are +7 rows, so I have tried this:

frames = []
for x in start_positions:
    frames.append(df.iloc[start_positions[x] : start_positions[x]+7])

However is throwing:

IndexError: index 6 is out of bounds for axis 0 with size 5

Which I don’t quite understand as this works if I manually increment through start_positions.

Each of the chunks represents a year of data and each column represents a different category. So the aim is to pull out the data and store it in separate locations corresponding to the year. — Maverick
– Maverick, Commented Jan 21, 2020 at 9:26
for x in start_positions: x are not indices! You use start_positions[x] , thus you see your error. Forget the dataframe, your issue occurs with you trying to index the list itself. — Paritosh Singh
– Paritosh Singh, Commented Jan 21, 2020 at 9:32
Does this answer your question? Python Loop: List Index Out of Range — Paritosh Singh
– Paritosh Singh, Commented Jan 21, 2020 at 9:35

eddys · Accepted Answer · 2020-01-21 09:32:47Z

1

The code has problem right from the start in the for loop I think. Look at start_positions[x] in frames.append(df.iloc[start_positions[x] : start_positions[x]+7]). The value of x in the for loop starts from 6 but the maximum index start_positionscan have is 4 since len(start_positions)=5

@Maverick , I think what you may want to do is remove start_positions and have something like this (but didnt test the code)

for x in start_positions:
    frames.append(df.iloc[x : x+7])

edited Jan 21, 2020 at 9:32

answered Jan 21, 2020 at 9:26

eddys

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nucsit026 · Accepted Answer · 2020-01-21 09:34:02Z

1

Try to use for x in range(len(start_positions)) instead of for x in start_positions as:

frames = []
for x in range(len(start_positions)):
    print(start_positions[x],":",start_positions[x]+7)

It results:

answered Jan 21, 2020 at 9:34

nucsit026

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Vishakha Lall · Accepted Answer · 2020-01-21 09:39:09Z

0

Another possible solution would be to use:

frames = []
for x in start_positions:
    frames.append(df.iloc[x:x+7])

x is an element of start_positions and can be accessed as is, had it been an index it would be used the way you did.

answered Jan 21, 2020 at 9:39

Vishakha Lall

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