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Tutorial Reference

Python NumPy: How to Convert a NumPy Array to Pandas Series

Learn how to convert a NumPy array to a Pandas Series with custom indexing, data types, and practical examples for data analysis.

Converting NumPy arrays to Pandas Series adds labeled indexing, built-in missing data handling, and rich statistical methods. The conversion is straightforward and preserves the underlying data efficiently.

Basic Conversion

Pass the array directly to pd.Series():

import numpy as np
import pandas as pd

arr = np.array([10, 20, 30, 40])
series = pd.Series(arr)

print(series)

Output:

0    10
1    20
2    30
3    40
dtype: int64

Adding Custom Index

Assign meaningful labels instead of default integer indices:

import numpy as np
import pandas as pd

arr = np.array([10, 20, 30, 40])

series = pd.Series(arr, index=['Q1', 'Q2', 'Q3', 'Q4'])
print(series)

Output:

Q1    10
Q2    20
Q3    30
Q4    40
dtype: int64

Label-Based Access

import numpy as np
import pandas as pd

arr = np.array([100, 200, 300])
series = pd.Series(arr, index=['A', 'B', 'C'])

print(series['A'])       # 100
print(series['B':'C'])   # B: 200, C: 300

print(series.iloc[0])    # 100

Output:

100
B    200
C    300
dtype: int64
100

Adding a Name

Give the Series a descriptive name:

import numpy as np
import pandas as pd

arr = np.array([1500, 2300, 1800])

series = pd.Series(
    arr,
    index=['Jan', 'Feb', 'Mar'],
    name='Monthly Sales'
)

print(series)

Output:

Jan    1500
Feb    2300
Mar    1800
Name: Monthly Sales, dtype: int6

Specifying Data Type

Control the Series dtype explicitly:

import numpy as np
import pandas as pd

arr = np.array([1, 2, 3])

series_float = pd.Series(arr, dtype='float64')
print(series_float.dtype)  # float64

series_str = pd.Series(arr, dtype='str')
print(series_str)

Output:

float64
0    1
1    2
2    3
dtype: object

Why Use Series Over Arrays?

Feature NumPy Array Pandas Series
Index type Integer only Any hashable labels
Missing data Manual handling Built-in NaN support
Alignment By position By label (automatic)
Statistics Basic (mean, std) Rich (describe, value_counts)
String methods Limited Full .str accessor
Datetime methods Limited Full .dt accessor

Practical Comparison

import numpy as np
import pandas as pd

arr = np.array([10, 20, 30, 40, 50])
series = pd.Series(arr, index=['a', 'b', 'c', 'd', 'e'])

print(series.describe())
print()

data = np.array(['A', 'B', 'A', 'C', 'A', 'B'])
print(pd.Series(data).value_counts())

Output:

count     5.000000
mean     30.000000
std      15.811388
min      10.000000
25%      20.000000
50%      30.000000
75%      40.000000
max      50.000000
dtype: float64

A    3
B    2
C    1
Name: count, dtype: int64

Memory Sharing Behavior

By default, Series may share memory with the source array:

import numpy as np
import pandas as pd

arr = np.array([1, 2, 3])
series = pd.Series(arr)

arr[0] = 99
print(series[0])  # 99

arr = np.array([1, 2, 3])
series = pd.Series(arr.copy())

arr[0] = 99
print(series[0])  # 1 (unchanged)

Output:

99
1

Converting Different Array Types

Multi-dimensional Arrays

Flatten first or select a column:

import numpy as np
import pandas as pd

arr_2d = np.array([[1, 2], [3, 4], [5, 6]])

series_flat = pd.Series(arr_2d.flatten())
print(series_flat)  # 0:1, 1:2, 2:3, 3:4, 4:5, 5:6
print()

series_col = pd.Series(arr_2d[:, 0])  # First column
print(series_col)   # 0:1, 1:3, 2:5

Output:

0    1
1    2
2    3
3    4
4    5
5    6
dtype: int64

0    1
1    3
2    5
dtype: int64

Datetime Arrays

import numpy as np
import pandas as pd

dates = np.array(['2024-01-01', '2024-02-01', '2024-03-01'], dtype='datetime64')

series = pd.Series(dates)
print(series.dt.month)  # Access datetime properties

Output:

0    1
1    2
2    3
dtype: int32

Practical Examples

Time Series Data

import numpy as np
import pandas as pd

prices = np.array([150.25, 152.30, 149.80, 155.00])
dates = pd.date_range('2024-01-01', periods=4)

stock = pd.Series(prices, index=dates, name='AAPL')
print(stock)

returns = stock.pct_change()
print(f"\nDaily returns:\n{returns}")

Output:

2024-01-01    150.25
2024-01-02    152.30
2024-01-03    149.80
2024-01-04    155.00
Freq: D, Name: AAPL, dtype: float64

Daily returns:
2024-01-01         NaN
2024-01-02    0.013644
2024-01-03   -0.016415
2024-01-04    0.034713
Freq: D, Name: AAPL, dtype: float64

Categorical Data with Counts

import numpy as np
import pandas as pd

responses = np.array(['Yes', 'No', 'Yes', 'Yes', 'No', 'Maybe'])
series = pd.Series(responses)

print(series.value_counts())
print(f"\nMode: {series.mode()[0]}")

Output:

Yes      3
No       2
Maybe    1
Name: count, dtype: int64

Mode: Yes

Handling Missing Data

import numpy as np
import pandas as pd

arr = np.array([1.0, np.nan, 3.0, np.nan, 5.0])
series = pd.Series(arr, index=['a', 'b', 'c', 'd', 'e'])

print(f"Count (non-null): {series.count()}")   # 3
print(f"Mean (ignores NaN): {series.mean()}")  # 3.0
print(f"Filled:\n{series.fillna(0)}")

Output:

import numpy as np
import pandas as pd

arr = np.array([1.0, np.nan, 3.0, np.nan, 5.0])
series = pd.Series(arr, index=['a', 'b', 'c', 'd', 'e'])

print(f"Count (non-null): {series.count()}")  # 3
print(f"Mean (ignores NaN): {series.mean()}")  # 3.0
print(f"Filled:\n{series.fillna(0)}")

Quick Reference

Goal Code
Basic conversion pd.Series(arr)
With labels pd.Series(arr, index=['a', 'b'])
With name pd.Series(arr, name='Sales')
With dtype pd.Series(arr, dtype='float64')
Independent copy pd.Series(arr).copy()
From 2D column pd.Series(arr_2d[:, 0])

Summary

  • Use pd.Series(arr) for quick conversion from NumPy arrays.
  • Add index for labeled access and name for descriptive identification.
  • The Series provides richer functionality than arrays-including automatic alignment, missing data handling, and comprehensive statistical methods-making it ideal for data analysis tasks.
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