在现有的CSV中添加第三列

Question

I have a CSV file with 2 Columns (x,y) and 5653 rows formated like this

0,0
1,0
2,0
3,0
4,0
5,0
....
102,0
102,1
101,1
....
0,1
0,2
1,2
....

Now I want to add a third column to it out of another csv with meassured values eg -89 etc those are mean values. these are also 5653 rows and its the first column of that file? Now how can I read the first file read the second file and put it like this

0,0,-89
1,0,-89
2,0,-89
3,0,-89
4,0,-90
5,0,-90
6,0,-89
7,0,-89
8,0,-89
9,0,-89

So I want the values to be the same just in one CSV

Answer 1

You can use the csv module which unlike pandas does not require you to install any third-party libraries. You can just zip the two readers:

import csv

with open('in1.csv') as fin1:
    with open('in2.csv') as fin2:
        with open('out.csv') as fout:
            r1 = csv.reader(fin1)  # iterator over lists of strings
            r2 = csv.reader(fin2)
            w = csv.reader(fout)
            for row1, row2 in zip(r1, r2):
                w.writerow(row1 + row2[:1])  # row from 1 + first column from 2

Answer 2

You could use the library pandas which is build to work with tabular data. typical workflow:

import pandas as pd
df1 = pd.read_csv("your_path") # df is a shorthand for dataframe, a name for tabular data.

df2 = pd.read_csv("csv2")

# concanating: http://pandas.pydata.org/pandas-docs/stable/merging.html
result = pd.concat([df1, df2], axis=1) # join by row, not by column
result.to_csv("path")