markdown pandas.DataFrameとnumpy.ndarrayを相互変换

Posted 2021-05-06

pandas.DataFrame->numpy.ndarray
```
import numpy as np
import pandas as pd

df = pd.DataFrame(data=[[1, 2, 3], [4, 5, 6]], columns=['a', 'b', 'c'])
print(df)
#    a  b  c
# 0  1  2  3
# 1  4  5  6

a_df = df.values
print(a_df)
# [[1 2 3]
#  [4 5 6]]

print(type(a_df))
# <class 'numpy.ndarray'>

print(a_df.dtype)
# int64
```

numpy.ndarray->pandas.DataFrame
```
a = np.arange(12).reshape((4, 3))
print(a)
# [[ 0  1  2]
#  [ 3  4  5]
#  [ 6  7  8]
#  [ 9 10 11]]

df = pd.DataFrame(a)
print(df)
#    0   1   2
# 0  0   1   2
# 1  3   4   5
# 2  6   7   8
# 3  9  10  11
```