Python: Reading CSV file and plotting a scatter

Question

I've written a script to compute large csv files in dimensions: 27000 rows x 22 column. How can I read in the CSV file in order to use it in matplotlib in a scattered plot like the one in this thread?

axis range in scatter graphs

The concept of generating a scatter plot is understood. Attempts have been made to parse csv file by e.g.:

data=csv.reader(open('some_file.csv, 'rb'), delimiter='|', quotechar='"')

but without success.

What -- specifically -- does "but without success" mean? Can you provide error messages or other indications of what's wrong? We can't really guess. — S.Lott
– S.Lott, Commented Feb 27, 2012 at 22:46
We do need more information, but there's also a syntax error in your code as posted here: 'somefile.csv needs a closing single quote. Was that just a typo? — Mike
– Mike, Commented Feb 27, 2012 at 22:55
@Mike: Without an actual error message, that could very well the problem. Or. The problem could be that data is only a reader, not the actual data that's desired. — S.Lott
– S.Lott, Commented Feb 27, 2012 at 23:37
apologies for the late response. I did two massive faults: 1st-I've selected the wrong delimiter, the 2nd mistake was marcus and dm pointed to it: I've not had in mind that data is a file-like object...and probably a 3rd mistake: I haven't been any precise about the problems I had blush. — Daniyal
– Daniyal, Commented Feb 28, 2012 at 0:21

kechap · Accepted Answer · 2012-02-27 22:39:30Z

9

Here is a quick solution

def getColumn(filename, column):
    results = csv.reader(open(filename), delimiter="\t")
    return [result[column] for result in results]

and then you can use it like this

time = getColumn("filename",0)
volt = getColumn("filaname",1)

plt.figure("Time/Volt")
plt.xlabel("Time(ms)")
plt.ylabel("Volt(mV)")
plt.plot(time,volt)

answered Feb 27, 2012 at 22:39

kechap

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Comments

dm03514 · Accepted Answer · 2012-02-27 22:40:39Z

1

Is that the correct delimiter? Did you read the documentation? http://docs.python.org/library/csv.html

data is a file-like object. you must iterate over it to access the data. each line is a list as marcus points out in his example.

answered Feb 27, 2012 at 22:40

dm03514

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