Turn repeat-sales data into sales pairs that are suitable for making repeat-sales matrices.
Arguments
- period
A vector that gives the time period for each sale. Usually a date vector, or a factor with the levels in chronological order, but other values are possible if they can be sorted in chronological order (i.e., with
order()).- product
A vector that gives the product identifier for each sale. Usually a factor or vector of integer codes for each product.
- match_first
Should products in the first period match with themselves (the default)?
Value
A numeric vector of indices giving the position of the previous sale
for each product, with the convention that the previous sale for the
first sale is itself if match_first = TRUE, NA otherwise. Ties are
resolved according to the order they appear in period.
Note
order() is the workhorse of rs_pairs(), so performance can be
sensitive to the types of period and product, and can be slow for large
character vectors.
See also
rs_matrix() for using sales pairs to make a repeat-sales index.
rtCreateTrans() in the hpiR package for a feature-rich but
slower and less flexible function to make sales pairs.
Examples
# Make sales pairs
x <- data.frame(
id = c(1, 1, 1, 3, 2, 2, 3, 3),
date = c(1, 2, 3, 2, 1, 3, 4, 1),
price = c(1, 3, 2, 3, 1, 1, 1, 2)
)
pairs <- rs_pairs(x$date, x$id)
x[c("date_prev", "price_prev")] <- x[c("date", "price")][pairs, ]
x
#> id date price date_prev price_prev
#> 1 1 1 1 1 1
#> 2 1 2 3 1 1
#> 3 1 3 2 2 3
#> 4 3 2 3 1 2
#> 5 2 1 1 1 1
#> 6 2 3 1 1 1
#> 7 3 4 1 2 3
#> 8 3 1 2 1 2