This function returns a value (or vector of values) of the value index
Usage
value_index(data, start, end, interval = FALSE)
Value
The function returns a value (or vector of values) of the value index. The value index is calculated as sum of expenditures from period end divided by sum of expenditures from period start.
Arguments
data
The user's data frame with information about sold products. It must contain columns: time (as Date in format: year-month-day,e.g. '2020-12-01'), prices (as positive numeric), quantities (as positive numeric) and prodID (as numeric, factor or character).
start
The base period (as character) limited to the year and month, e.g. "2020-03".
end
The research period (as character) limited to the year and month, e.g. "2020-04".
interval
A logical value indicating whether the function is to compare the research period defined by end to the base period defined by start (then interval is set to FALSE) or all fixed base indices are to be calculated. In this latter case, all months from the time interval <start,end> are considered and start defines the base period (interval is set to TRUE).
References
(2004). Consumer Price Index Manual. Theory and practice. ILO/IMF/OECD/UNECE/Eurostat/The World Bank, International Labour Office (ILO), Geneva.