Set dataframe row value to a numpy array value

Question

Edited version of original post

I have a dataframe that's entirely populated with NaN. Specifically:

print(histPrice['Allocation %'])

[Output]: 
 Symbols    SPY  GLD  TLT   MA   QQQ      TIP
Date                                         
2019-11-01  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-31  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-30  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-29  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-28  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-25  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-24  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-23  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-22  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-21  NaN  NaN  NaN   NaN  NaN      NaN
2019-10-18  NaN  NaN  NaN   NaN  NaN      NaN

I have the following numpy array:

x = np.array([0.1,0.3,0.2,0.1,0.1,0.2])

I tried assigning the array to 2019-10-30 row by:

histPrice['Allocation %'].iloc[2] = x

as well as

histPrice['Allocation %'].iloc[2,:] = x

Yet, both result in:

print(histPrice['Allocation %'].iloc[2])

[Output]: 
 Symbols
SPY       NaN
GLD       NaN
TLT       NaN
MA        NaN
QQQ       NaN
TIP       NaN
Name: 2019-10-30 00:00:00, dtype: float64

I'm baffled as to why it's still outputting NaN. Any help would be greatly appreciated.

are u trying to replace every third row of table with np array? — Jjj
– Jjj, Commented Nov 4, 2019 at 3:44
@Tserenjamts i'm just trying to replace a specific row with an array — Drive2blue
– Drive2blue, Commented Nov 4, 2019 at 13:37
@Drive2blue but it looks like histPrice['Allocation %'] is a dataframe as well — aprilangel
– aprilangel, Commented Nov 5, 2019 at 3:39

U13-Forward · Accepted Answer · 2021-12-20 09:08:07Z

2

You need loc with indexing of df.index:

histPrice.loc[df.index[2], 'Allocation %'] = x

answered Dec 20, 2021 at 9:08

U13-Forward

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Comments

BENY · Accepted Answer · 2019-11-04 03:52:36Z

0

You should do

df.iloc[2,:]=a[0]
df
Out[142]: 
        Stock: Bond: Gold:
2/01/19    NaN   NaN   NaN
1/31/19    NaN   NaN   NaN
1/30/19    33%   33%   33%
1/29/19    NaN   NaN   NaN

answered Nov 4, 2019 at 3:52

BENY

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1 Comment

Drive2blue Over a year ago

This didn't work. See section "Additional Details" in my updated post

Rick · Accepted Answer · 2019-11-05 03:05:54Z

0

If you want to update the whole row with your numpy array, you should be able to use:

x = np.array([2,3,1])
df.iloc[2]= x

        Stock Bond Gold
2/01/19   NaN  NaN  NaN
1/31/19   NaN  NaN  NaN
1/30/19     2    3    1
1/29/19   NaN  NaN  NaN

This will update the row with each value of the array, and not just the first value.

I am curious if this will work for you?

import pandas as pd
import numpy as np
df = pd.DataFrame(columns=['Stock','Bond','Gold'], index=['2/01/19','1/31/19','1/30/19','1/29/19'])
histPrice = {}
histPrice['Allocation %'] = df
x = np.array([2,3,1])
histPrice['Allocation %'].iloc[2] = x 
print(histPrice['Allocation %'].iloc[2])

edited Nov 5, 2019 at 3:05

answered Nov 4, 2019 at 4:02

Rick

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11 Comments

Drive2blue Over a year ago

This didn't work. See section "Additional Details" in my updated post

Rick Over a year ago

@drive2blue It looks like you are trying to assign the array to one column histPrice['Allocation %'], and not a row.

Rick Over a year ago

@drive2blue do you have a dataframe saved in a dictionary?

Rick Over a year ago

@Drive2blue Based on your updated question, I am wondering if you have one or more dataframes stored in a dictionary. Is there a chance you are updating the wrong dataframe (I only ask because you reference two different dataframes in your updated question: histPrice['Allocation %'], histPrice['RP Allocation %'])?

Rick Over a year ago

@Drive2blue I was wondering if there was a nested dataframe, and I was even looking into storing dataframes within dataframes as that is a new concept for me. I'm glad I was still able to help though.

|

aprilangel · Accepted Answer · 2019-11-06 03:41:08Z

0

From the description, you are storing a dataframe in another single row dataframe.

And when doing below, You are setting an value in the copy of your dataframe.

histPrice['Allocation %'].iloc[2] = x

Instead, try: (you can replace the 0 with your index)

histPrice.loc[0, 'Allocation %'].iloc[2] = x

edited Nov 6, 2019 at 3:41

answered Nov 5, 2019 at 16:56

aprilangel

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2 Comments

Drive2blue Over a year ago

hmmm, I tried your suggestion but got KeyError: 'Allocation %' Instead, I tried histPrice.loc[ : , 'Allocation %'].iloc[2] = x but that resulted in ValueError: setting an array element with a sequence :(

aprilangel Over a year ago

@Drive2blue don't use array, set x as a list. should be fine =)

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