Question

So i have this csv file and one collumn looks like this:

1022
1040
1042
1035
11728
1036
1022
1040
1042
1035
11728
1036
1022
1040
1042
1035
11728

Now i need to count how oftend a number occurs. I need this to make a graphic picture with matplotlib. So the graphic will show how much a number occurs (in this situation it’s a event id)

so far i only have the code to print that row…

my_reader = csv.reader(open(csvpath))
for col in my_reader:
      print col[3]

how do i count how often a number in that specific collumn occurs?

Answer 1

Just create a mapping from number to count. The collections.Counter() class makes that easiest:

import collections

counts = collections.Counter()
for row in my_reader:
    counts[row[3]] += 1

Using a collections.defaultdict is also an option:

counts = collections.defaultdict(int)
for row in my_reader:
    counts[row[3]] += 1

or you can use a normal dict:

counts = {}
for row in my_reader:
    counts[row[3]] = counts.get(row[3], 0) + 1