Yet another list csv file in Python question

Question

I have a file csv file in this format, I would like to generate the average for each step:

elapsed,label
120,Step 01
260,Step 02
113,Step 03
100,Step 01
200,Step 02
103,Step 03

but am having a hard time figuring the lists out. The Python script that I am using is:

for file in sys.argv[1:]:
  for row in csv.DictReader(open(file)):
    label = row['label']
    elapsed = row['elapsed']
    print elapsed,label

I've tried

label.append(row['elapsed']) and label.append('elapsed'), but in each case I get this error

AttributeError: 'str' object has no attribute 'append'

I am unsure how to get past this error. I'm new to Python, so perhaps I am missing something in the way lists work? If I can get a list like [120,100] for step 01, I can easily sum and average it, but it is the list creation part that I am stuck on.

Edit: Sum of result list

Now, I have this:

  for item in result:
    for n in result[item]:
      int(n)
      print sum(float(result[item][n]))

but get this error

TypeError: list indices must be integers, not str

But "n" is an integer already, no ... ? Or is this referring to "item"? I think I am more confused now than before.

Pablo · Accepted Answer · 2011-07-28 17:34:55Z

3

I believe this should achieve what you're attempting:

result = dict()
for file in sys.argv[1:]:
  for row in csv.DictReader(open(file)):
    label = row['label']
    elapsed = float(row['elapsed'])
    if label in result:
      result[label].append(elapsed)
    else:
      result[label] = [elapsed]

totals = dict((label, sum(values)) for label, values in result.iteritems())

After executing this, result will contain the lists in the format you wanted.

edited Jul 28, 2011 at 17:34

answered Jul 27, 2011 at 22:12

Pablo

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6 Comments

schlamar Over a year ago

Additionally, you can get the step number as an integer by int(label[5:]).

agf Over a year ago

You want a defaultdict here, as I used in my answer.

Pablo Over a year ago

@agf thanks! I'm still learning Python myself and I didn't know about it.

KM. Over a year ago

Thanks @Pablo. I just updated my question, as now I am seeing another error ... perhaps I underestimated this exercise ... what am I missing ... ?

KM. Over a year ago

@ms4py, I'm sorry I don't know what you mean by int(label[5:]) ... could you perhaps put that in context ... ?

|

agf · Accepted Answer · 2011-07-28 14:12:17Z

2

If what you want is to make lists,

from collections import defaultdict
steps = defaultdict(list)

for file in sys.argv[1:]:
  for row in csv.DictReader(open(file)):
    steps[row['label']].append(row['elapsed'])

averages = dict((key, sum(value)) for key, value in steps.iteritems())

Will give you the averages.

What you're doing is attempting to add the string in row['elapsed'] to the string in label, but strings are immutable so can't be appended to. You can join them with string1 + string2 or `''.join((string1, string2)).

EDIT: Also, for your new error, See the last line of my code, or, try:

averages = {}
for item in result.iteritems():
    print item[0], sum(item[1])

edited Jul 28, 2011 at 14:12

answered Jul 27, 2011 at 22:12

agf

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2 Comments

schlamar Over a year ago

Not really a solution for what he wants to achieve. You should have noticed that his approach is totally wrong.

KM. Over a year ago

Thanks @agf, I get this error when running this script: TypeError: first argument must be callable. I then removed [] from defaultdict([]), and then get this: KeyError:'Step 01'

halfer · Accepted Answer · 2019-04-15 07:46:32Z

0

(Posted solution on behalf of the question author).

Many thanks to @Pablo, @agf & @ms4py. Your input brought me to this.

result = dict()
av = []
idx = []
for file in sys.argv[1:]:
  for row in csv.DictReader(open(file)):
    label = row['label']
    elapsed = row['elapsed']
    if label in result:
      result[label].append(elapsed)
    else:
      result[label] = [elapsed]    
  for i in sorted (result.iterkeys()):
    s = sum(int(v) for v in result[i])
    a = s/float(len(result[i]))

answered Apr 15, 2019 at 7:46

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