如何在python中如下转换数据？

Question

I have some data in the following format in a csv file.

   Id   Category
    1   A
    2   B
    3   C
    4   B
    5   C
    6   d

I'd like to convert it into the below format and save it another csv file

Id  A   B   C   D   E
1   1   0   0   0   0
2   0   1   0   0   0
3   0   0   1   0   0
4   0   1   0   0   0
5   0   0   1   0   0
6   0   0   0   1   0

Answer 1

Try with pd.get_dummies()

>> df = pd.read_csv(<path_to_file>, sep=',', encoding='utf-8', header=0)

>> df
   Id   Category
0   1          A
1   2          B
2   3          C
3   4          B
4   5          C
5   6          d

>> pd.get_dummies(df.Category)

This will encode Category and give you new columns:

A B C d

But will not 'fix' d -> D and will not give you any columns that can not be deduced from the values you have in Category .

I suggest you check the solution posted in the comment earlier for that.

EDIT

# Load data from .CSV with pd.read_csv() as demonstrated above

In [13]: df
Out[13]: 
  Category  Id
0        A   1
1        B   2
2        C   3
3        B   4
4        C   5
5        D   6

## One-liner for hot-encoding, then concatenating to original dataframe 
## and finally dropping the old column 'Category', you can skip the 
## last part if you want to keep original column as well.
In [14]: df = pd.concat([df, pd.get_dummies(df.Category)], axis=1).drop('Category', axis=1)

In [15]: df
Out[15]: 
   Id    A    B    C    D
0   1  1.0  0.0  0.0  0.0
1   2  0.0  1.0  0.0  0.0
2   3  0.0  0.0  1.0  0.0
3   4  0.0  1.0  0.0  0.0
4   5  0.0  0.0  1.0  0.0
5   6  0.0  0.0  0.0  1.0

## Write to file
In [16]: df.to_csv(<output_path>, sep='\t', encoding='utf-8', index=None)

As you can see this is not the Transpose, only the result of the hot-encoding of the Category column is added to each row.

Whether Excel accepts the final data or not, there's not much you can do with Pandas about this, unfortunately.

I hope this helps.

Answer 2

Use a pivot table (updated to include .csv read/write functionality):

import pandas as pd
path = 'the path to your file'
df = pd.read_csv(path)

# your original dataframe
# Category  Id
# 0        A   1
# 1        B   2
# 2        C   3
# 3        B   4
# 4        C   5
# 5        D   6

# pivot table
df.pivot_table(index=['Id'], columns='Category', fill_value=0, aggfunc='size')

# save to file
df.to_csv('path\filename.csv') #e.g. 'C:\\Users\\you\\Documents\\filename.csv'

---

OUTPUT:

Category  A  B  C  D
Id                  
1         1  0  0  0
2         0  1  0  0
3         0  0  1  0
4         0  1  0  0
5         0  0  1  0
6         0  0  0  1