Converts each series (column) in an rwl-style data.frame
to z-scores by subtracting the mean and dividing by the standard deviation.
Examples
rwl <- trs_pseudo_rwl(n_series = 3, series_length = 50, end_date = 1990)
z_rwl <- trs_zscore(rwl)
apply(z_rwl, 2, mean, na.rm = TRUE) # should be ~0
#> trs_1 trs_2 trs_3
#> -3.038975e-16 4.366559e-16 2.591330e-16
apply(z_rwl, 2, sd, na.rm = TRUE) # should be ~1
#> trs_1 trs_2 trs_3
#> 1 1 1