Sorting a csv file in Python with sorted() returns values in programmer DESC order, not time DESC order

I'm not doing anything overly complex I believe. I'm presorting a large csv data file because it is full of data that arrives in random time order. The index is correct, but the return formatting is off.

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    sortedList=sorted(reader,key=operator.itemgetter(1))

So instead of sorting like [-100 -10 -1 0 10 100 5000 6000]; I get [-1 -10 -100 0 100 5000 60]

I tried both the lambda function examples and itemgetter, but I don't really know where to go from there.

Thanks for the help.

The answer to my question is in the comments. The numerical value was being sorted as a string and not a number. I didn't know that I could specify the data type of the key in sorted(). This code works as I intended:

    sortedList=sorted(reader,key=lambda x:float(x[1]))

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Just from the output you see there, it looks like these are being sorted as strings rather than as numbers.

So you could do:

sortedList=sorted(reader, key=lambda t: int( t[1] ))

or

sortedList=sorted(reader, key=lambda t: float( t[1] ))

Or better, try to ensure that the sequence reader gets populated with numbers, rather than strings, when it's created, perhaps using QUOTE_NONNUMERIC as a fmtparam for the reader (see http://docs.python.org/library/csv.html#csv.QUOTE_NONNUMERIC).

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It looks like "reader" yields strings, and what you want is integers. You could try something like :

    sorted(reader, key=lambda x: float(x[1]))

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it looks like your numbers are getting sorted alphabetically (as strings) rather than numerically:

>>> sorted([10,2000,30])
[10, 30, 2000]
>>> sorted(['10','2000','30'])
['10', '2000', '30']

To fix this, you can pass a numeric sort:

def numeric_compare(x, y):
    return int(x)-int(y)

>>> sorted(['10','2000','30'],cmp=numeric_compare)
['10', '30', '2000']

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It looks like your list is being sorted as strings rather than numbers. When you read in your CSV file, it is still text and must be converted to integers first.

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I like compose:

from operator import itemgetter

def compose(f, g):
    return lambda *a, **k: g(f(*a, **k))

sortedList = sorted(reader, key=compose(itemgetter(1), float))