How to read numbers in python from csv file?

Question

I have a csv file and I have to compute the mean for some of the columns. That's how I did:

file=csv.reader(open('tab.csv','r'))
n=[]
for row in file:
    n.append(row[8])

So I have a list of string : n=['','','1.58'...] How can I convert these to float? I tried with :

n_values=np.array(n)
n_values[n=='']='0'
values=n_values.astype(np.float)
np.mean(values)

But the mean is not correct because I should skip the empty strings not counting. Thank for your help!

Answer 1

Just cast as you append:

 n.append(float(row[8]))

If there are empty strings catch those before appending.

try:
    n.append(float(row[8]))
except ValueError:
   continue

Or you might want to try pandas, in particular pandas.read_csv:

import pandas as pd

df = pd.read_csv("in.csv")
print(df["col_name"].mean())