https://www.visidata.org/docs/plugins/

vd_dateutil.py

from typing import Union, Callable
import types

# 3p libraries
from dateutil.relativedelta import relativedelta  # type: ignore
from visidata import Sheet, Column, SettableColumn, asyncthread, vd  # type: ignore
import pandas as pd  # type: ignore


def get_frequency(column: Column,
                  f: Union[str, Callable],
                  column_name: str):
    sheet = column.sheet
    current_index = sheet.cursorColIndex
    frequency_column = SettableColumn(column_name)
    sheet.addColumn(frequency_column,
                    index=current_index + 1)

    for r in sheet.rows:
        value = r.get(column.name)
        if isinstance(f, types.FunctionType):
            value = f(pd.Period(value))
        elif value:
            value = pd.Period(value, freq=f)
        frequency_column.setValue(r, value)


@Column.api
@asyncthread
def quarter(column: Column):
    get_frequency(column, f='Q', column_name='quarter')


@Column.api
@asyncthread
def year(column: Column):
    get_frequency(column, f='Y', column_name='year')


@Column.api
@asyncthread
def week(column: Column):
    get_frequency(column, f='W', column_name='week')


@Column.api
@asyncthread
def day(column: Column):
    get_frequency(column,
                  f=lambda x: x.strftime('%A'),
                  column_name='day')


@Column.api
@asyncthread
def period(column: Column):
    get_frequency(column,
                  f=lambda x: x,
                  column_name='period')


@Column.api
def diff(column: Column):
    sheet = column.sheet
    column_names = [x.name for x in sheet.columns]

    def to_datetime(value):
        return (pd.Period(value)
                .to_timestamp()
                .to_pydatetime()
                .replace(second=0, microsecond=0)
                if value else None)

    def completer(value, state):
        options = [x for x in column_names if x.startswith(value)]
        return options[state % len(options)] if options else None

    input_column = vd.input('date: ', completer=completer)
    if input_column not in column_names:
        return None

    diff_column = SettableColumn('diff')
    diff_seconds_column = SettableColumn('diff_total_seconds', type=int)
    index = sheet.cursorColIndex + 1
    sheet.addColumn(diff_column, index=index)
    sheet.addColumn(diff_seconds_column, index=index)

    for r in sheet.rows:
        a = to_datetime(r.get(column.name))
        b = to_datetime(r.get(input_column))

        if a and b:
            diff = relativedelta(a, b)
            diff_str = f'{diff.years} years(s), {diff.months} month(s), {diff.days} day(s)'
            diff_seconds = (a - b).total_seconds()

            diff_column.setValue(r, diff_str)
            diff_seconds_column.setValue(r, diff_seconds)


# we'll use @ as the prefix since that's the key vd uses to force a date type
Sheet.addCommand(None, '@day', 'cursorCol.day()')
Sheet.addCommand(None, '@diff', 'cursorCol.diff()')
Sheet.addCommand(None, '@period', 'cursorCol.period()')
Sheet.addCommand(None, '@quarter', 'cursorCol.quarter()')
Sheet.addCommand(None, '@week', 'cursorCol.week()')
Sheet.addCommand(None, '@year', 'cursorCol.year()')