How to Retrieve the String Alias of Time Series Frequency in Pandas

πŸ’‘ Problem Formulation: When working with time series data in Python’s Pandas library, one may need to determine the frequency of a given Period object. This process involves retrieving the string alias that represents the period’s frequency, which can be daily (‘D’), monthly (‘M’), annually (‘A’), and so on. For example, given a Period object representing the month of January 2021, the desired output would be the string ‘M’ denoting its monthly frequency.

Method 1: Using the freqstr Attribute

This method utilizes the freqstr attribute of a Pandas Period object to return the string alias of the Period’s frequency. It’s a straightforward and Pythonic way to access the frequency information without additional function calls.

Here’s an example:

import pandas as pd

# Create a Period object for January 2021
monthly_period = pd.Period('2021-01', freq='M')
# Retrieve the string alias of the Period's frequency
frequency_alias = monthly_period.freqstr

print(frequency_alias)

Output:

'M'

This code snippet demonstrates the simplicity of achieving our goal. A Period object is created with a specified monthly frequency (‘M’), and the freqstr attribute of this object directly provides the string alias.

Method 2: Using the to_timestamp Function

By converting a Period object to a Timestamp with the to_timestamp method and accessing its freqstr, this method indirectly retrieves the frequency string alias.

Here’s an example:

import pandas as pd

# Create a Period object for January 2021
monthly_period = pd.Period('2021-01', freq='M')
# Convert to Timestamp and retrieve the frequency alias
frequency_alias = monthly_period.to_timestamp().freqstr

print(frequency_alias)

Output:

'M'

This code takes advantage of the fact that both Period and Timestamp objects carry frequency information. The to_timestamp function is used to convert the Period into a Timestamp, from which the freqstr is extracted.

Method 3: Using the asfreq Method

The asfreq method is used to convert the frequency of the Period object which also allows access to the freqstr attribute to retrieve the string alias.

Here’s an example:

import pandas as pd

# Create a Period object for January 2021
monthly_period = pd.Period('2021-01', freq='M')
# Convert the frequency and retrieve the frequency alias
frequency_alias = monthly_period.asfreq('M').freqstr

print(frequency_alias)

Output:

'M'

In this code snippet, the original Period object’s frequency is converted to the same frequency using asfreq. The resulting Period’s freqstr gives us the string alias.

Method 4: Using Period Index frequency Attribute

This method involves creating a PeriodIndex from a single Period object, allowing extraction of the frequency attribute, which can then be turned into a string.

Here’s an example:

import pandas as pd

# Create a PeriodIndex from a single Period object
period_index = pd.period_range('2021-01', periods=1, freq='M')
# Retrieve the frequency attribute and convert it to a string
frequency_alias = str(period_index.freq)

print(frequency_alias)

Output:

''

In this snippet, pd.period_range is used to make a PeriodIndex, which naturally holds a frequency attribute. However, note that this produces a slightly different string representation that is more descriptive than the simple alias.

Bonus One-Liner Method 5: Using freq.name Attribute

A fast and concise way to get the frequency alias is by accessing the name property of the freq attribute of a Period object.

Here’s an example:

import pandas as pd

# Create a Period object for January 2021
monthly_period = pd.Period('2021-01', freq='M')
# Retrieve the name of the frequency object
frequency_alias = monthly_period.freq.name

print(frequency_alias)

Output:

'M'

Here, we are directly accessing the name of the Period object’s frequency, making this a compact one-liner solution with no need for conversion or accessing intermediate properties.

Summary/Discussion

  • Method 1: Using freqstr Attribute. Straightforward. Produces exact frequency alias.
  • Method 2: Using to_timestamp Function. Indirect. Requires conversion to Timestamp.
  • Method 3: Using asfreq Method. Versatile. May convert to different frequencies if needed.
  • Method 4: Using Period Index frequency Attribute. Informative. Provides more detail than just an alias.
  • Bonus Method 5: One-Liner Using freq.name Attribute. Efficient. Least amount of coding required.