csv python questions
i am opening a csv file like this:
import csv
reader = csv.reader(open("book1.csv", "rb"))
for row in reader:
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how can i replace the value in column 3 with its log
and then save the result into a new csv?
Like this?
>>> input = "1,2,3\n4,5,6\n7,8,9".splitlines()
>>> reader=csv.reader(input)
>>> for row in reader:
... row[2] = log(float(row[2]))
... print ','.join(map(str,row))
...
1,2,1.09861228867
4,5,1.79175946923
7,8,2.19722457734
These links might help:
http://docs.python.org/library/csv.html#csv.writer
http://docs.python.org/tutorial/datastructures.html?highlight=array
Each row being returned by reader
is an array. Arrays in Python are 0 based (So to access the third entry in a row, you would use my_array[2]
)
That should help you on your way.
You should use the context manager WITH statement for files - cleaner, less code, obviates file.close() statements.
e.g.
import csv
import math
with open('book1.csv', 'rb') as f1,open('book2.csv', 'wb') as f2:
reader = csv.reader(f1)
writer = csv.writer(f2)
for row in reader:
row[2] = str(math.log(float(row[2])))
writer.writerow(row)
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