在 csv.reader 中访问数据

Question

I'm trying to access a csv file of currency pairs using csv.reader. The first column shows dates, the first row shows the currency pair eg.USD/CAD. I can read in the file but cannot access the currency pairs data to perform simple calculations.

I've tried using next(x) to skip header row (currency pairs). If i do this, i get a Typeerror: csv reader is not subscriptable.

path = x
file = open(path)
dataset = csv.reader(file, delimiter = '\t',)
header = next(dataset)
header

Output shows the header row which is

['Date,USD,Index,CNY,JPY,EUR,KRW,GBP,SGD,INR,THB,NZD,TWD,MYR,IDR,VND,AED,PGK,HKD,CAD,CHF,SEK,SDR']

I expect to be able to access the underlying currency pairs but i'm getting the type error as noted above. Is there a simple way to access the currency pairs, for example I want to use USD.describe() to get simple statistics on the USD currency pair.

How can i move from this stage to accessing the data underlying the header row?

Answer 1

try this example

import csv

with open('file.csv') as csv_file:
    csv_reader = csv.Reader(csv_file, delimiter='\t')
    line_count = 0
    for row in csv_reader:
        print(f'\t{row[0]} {row[1]} {row[3]}')

Answer 2

从标题行的输出中可以明显看出，列是逗号分隔而不是制表符分隔的，因此不应将delimiter = '\\t'传递给csv.reader ，而应让它使用默认分隔符',' ：

dataset = csv.reader(file)

Answer 3

Are you sure that your delimiter is '\\t' ? In first row your delimiter is ',' ... Anyway you can skip first row by doing file.readline() before using it by csv.reader :

import csv

example = """Date,USD,Index,CNY,JPY,EUR,KRW,GBP,SGD,INR,THB,NZD,TWD,MYR,IDR,VND,AED,PGK,HKD,CAD,CHF,SEK,SDR
1-2-3\tabc\t1.1\t1.2
4-5-6\txyz\t2.1\t2.2
"""

with open('demo.csv', 'w') as f:
    f.write(example)

with open('demo.csv') as f:
    f.readline()
    reader = csv.reader(f, delimiter='\t')
    for row in reader:
        print(row)
# ['1-2-3', 'abc', '1.1', '1.2']                                                                                                                                                                                                   
# ['4-5-6', 'xyz', '2.1', '2.2']

I think that you need something else... Can you add to your question:

• example of first 3 lines in your csv

• Example of what you'd like to access:

  • is using row[0] , row[1] enough for you?
  • or do you want "named" access like row['Date'], row['USD'] ,
  • or you want something more complex like data_by_date['2019-05-01']['USD']

Answer 4

If you need to elaborate some statistics pandas is your friend. No need to use the csv module, use pandas.read_csv .

import pandas

filename = 'path/of/file.csv'
dataset = pandas.read_csv(filename, sep = '\t') #or whatever the separator is

pandas.read_csv uses the first line as the header automatically.
To see statistics, simply do:

dataset.describe()

Or for a single column:

dataset['column_name'].describe()