I am interested in knowing how to convert a pandas dataframe into a NumPy array.
dataframe:
import numpy as np
import pandas as pd
index = [1, 2, 3, 4, 5, 6, 7]
a = [np.nan, np.nan, np.nan, 0.1, 0.1, 0.1, 0.1]
b = [0.2, np.nan, 0.2, 0.2, 0.2, np.nan, np.nan]
c = [np.nan, 0.5, 0.5, np.nan, 0.5, 0.5, np.nan]
df = pd.DataFrame({"A": a, "B": b, "C": c}, index=index)
df = df.rename_axis("ID")
gives
label A B C
ID
1 NaN 0.2 NaN
2 NaN NaN 0.5
3 NaN 0.2 0.5
4 0.1 0.2 NaN
5 0.1 0.2 0.5
6 0.1 NaN 0.5
7 0.1 NaN NaN
I would like to convert this to a NumPy array, as so:
array([[ nan, 0.2, nan],
[ nan, nan, 0.5],
[ nan, 0.2, 0.5],
[ 0.1, 0.2, nan],
[ 0.1, 0.2, 0.5],
[ 0.1, nan, 0.5],
[ 0.1, nan, nan]])
How can I do this?
As a bonus, is it possible to preserve the dtypes, like this?
array([[ 1, nan, 0.2, nan],
[ 2, nan, nan, 0.5],
[ 3, nan, 0.2, 0.5],
[ 4, 0.1, 0.2, nan],
[ 5, 0.1, 0.2, 0.5],
[ 6, 0.1, nan, 0.5],
[ 7, 0.1, nan, nan]],
dtype=[("ID", "<i4"), ("A", "<f8"), ("B", "<f8"), ("B", "<f8")])
or similar?
Convert pandas dataframe to NumPy array rename: Questions
Rename a dictionary key
5 answers
Is there a way to rename a dictionary key, without reassigning its value to a new name and removing the old name key; and without iterating through dict key/value?
In case of OrderedDict, do the same, while keeping that key"s position.
Answer #1
For a regular dict, you can use:
mydict[k_new] = mydict.pop(k_old)
This will move the item to the end of the dict, unless k_new was already existing in which case it will overwrite the value in-place.
For a Python 3.7+ dict where you additionally want to preserve the ordering, the simplest is to rebuild an entirely new instance. For example, renaming key 2 to "two":
>>> d = {0:0, 1:1, 2:2, 3:3}
>>> {"two" if k == 2 else k:v for k,v in d.items()}
{0: 0, 1: 1, "two": 2, 3: 3}
The same is true for an OrderedDict, where you can"t use dict comprehension syntax, but you can use a generator expression:
OrderedDict((k_new if k == k_old else k, v) for k, v in od.items())
Modifying the key itself, as the question asks for, is impractical because keys are hashable which usually implies they"re immutable and can"t be modified.
How to rename a file using Python
5 answers
I want to change a.txt to b.kml.
Answer #1
Use os.rename:
import os
os.rename("a.txt", "b.kml")
Rename multiple files in a directory in Python
5 answers
I"m trying to rename some files in a directory using Python.
Say I have a file called CHEESE_CHEESE_TYPE.*** and want to remove CHEESE_ so my resulting filename would be CHEESE_TYPE
I"m trying to use the os.path.split but it"s not working properly. I have also considered using string manipulations, but have not been successful with that either.
Answer #1
Use os.rename(src, dst) to rename or move a file or a directory.
$ ls
cheese_cheese_type.bar cheese_cheese_type.foo
$ python
>>> import os
>>> for filename in os.listdir("."):
... if filename.startswith("cheese_"):
... os.rename(filename, filename[7:])
...
>>>
$ ls
cheese_type.bar cheese_type.foo
