Convert CSV percentage strings to decimal fractions
Parse explicitly marked percentage values in Python, divide once by 100, and avoid confusing 12.5 percent with the fraction 12.5.
Example files included
All guidesDates & numbers
Untangle dates, decimal separators, and values that only look like numbers.
Check the underlying value and the source locale before changing the display.
Convert day/month dates without guessing ambiguous rows
Resolve ambiguous imported dates with an explicit day/month rule, a validation formula, and a downloadable example with invalid-date cases.
Example files included
Convert Unix timestamps: seconds or milliseconds?
Convert integer Unix timestamps to UTC in Python, require the documented unit, and preserve millisecond precision without float division.
Example files included
Find CSV numbers with too many decimal places
Check whether decimal CSV values fit a two-place scale without rounding them silently, and separate numeric scale from written trailing zeros.
Example files included
Fix dates that will not sort in Google Sheets
Diagnose text dates with ISNUMBER, convert a controlled date format in a helper column, and verify chronological order without separating records.
Example files included
Fix decimal commas and thousands separators in Excel
Convert imported numeric text using explicit decimal and grouping marks, preserve blanks, and avoid turning an ambiguous amount into the wrong number.
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Fix numbers stored as text without damaging identifiers
Diagnose numeric-looking text with ISNUMBER, convert quantity cells safely, preserve missing values, and keep identifiers such as 0012 unchanged.
Example files included
Group CSV dates by ISO week and the correct week-year
Use the ISO year together with the ISO week in Python so year-end dates do not split one reporting week across different labels.
Example files included
Normalize CSV timestamps with offsets to UTC
Parse offset-aware timestamp strings in Python and convert them to UTC without attaching an invented timezone to local clock values.
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Parse CSV durations longer than 24 hours
Convert H:MM:SS duration strings to total seconds in Python without treating them as times of day or wrapping after 24 hours.
Example files included
Parse parenthesized negative amounts in a CSV
Convert a confirmed accounting-style negative such as (12.50) to -12.50 in Python, while rejecting unbalanced or doubly signed values.
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Reject impossible calendar dates in a CSV
Validate strict YYYY-MM-DD date strings in Python, reject non-leap February 29 and overflow days, and keep invalid records for correction.
Example files included
Round CSV decimal values with an explicit tie rule
Use Decimal quantize in Python to round text amounts deliberately, and test halfway values that distinguish half-even from half-up.
Example files included
Sum CSV amounts by group with decimal arithmetic
Group decimal CSV amounts in Python, reject nonfinite values, and keep currencies separate so the resulting totals remain meaningful.
Example files included