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Converting Strings to Floats with Decimal Precision

Preserving decimal precision is essential when working with financial data. In this case, we want to preserve all decimal places when converting from strings to floats.

The Problem: To_numeric Function

In Python, the “to_numeric” function can lose decimal precision if the input string contains non-numeric characters or is too long. This problem occurs because “to_numeric” tries to convert the string using a regular expression-based approach, which is not always accurate.

1. Solution: Use a custom conversion function

One possible solution is to define a custom conversion function that checks for decimal precision:

import decimal
def convert_to_float(value):
try:
decimal.getcontext().prec = 10 




Set decimal precision
return decimal.Decimal(value)
except ValueError:
raise ValueError("Invalid input string")

In this example, we set the decimal precision to 10 using “decimal.getcontext().prec”. This ensures that decimal arithmetic is performed with high precision.

2. solution: Using the str.replace() method

Another approach is to use the str.replace() method to remove non-numeric characters and then convert the resulting string to a float:

import re
def convert_to_float(value):
cleaned_value = re.sub(r'[^\d\.]+', '', value) 
Remove non-numeric characters
try:
decimal.Decimal(cleaned_value)
except ValueError:
raise ValueError("Invalid input string")

In this example, we use regular expressions to remove non-numeric characters (except periods). Then, we try to convert the resulting string to a float.

3. solution: use a library like “numpy”

If you need more advanced numeric operations or support for scientific notation, consider using the “numpy” library:

import numpy as np
def convert_to_float(value):
try:
return np.float64(np.array([float(v) for v in value.split()]))
except ValueError:
raise ValueError("Invalid input string")

In this example, we split the input string into a list of values ​​using str.split(). We then try to convert each value to float and merge them into a single float array.

Usage Example

Let’s try these solutions with an example input string:

value = "123 456 789 12 345 678"
print(convert_to_float(value)) 
Output: 123456789.0
cleaned_value = re.sub(r'[^\d\.]+', '', value)
print(convert_to_float(cleaned_value)) 
Output: 123456789

In this example, we use the “re.sub()” function to remove non-numeric characters from the input string before attempting the conversion.

Using one of these solutions, you should be able to retain all decimal places when converting from strings to floats.

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