how to make calculation for y value in tooltip in sparkline in r

Question

I am trying to show ranking in line and increase in number means a decrease in rank. That's why to visualize this relation I multiple rank values with minus 1. However, in tooltip it shows up with minus sign and I can't make calculations in double curly braces. Code is below.

library(data.table)
library(sparkline)
library(tidyverse)
library(DT)

vec_line <- data.table(rank = c(3,2,6,7), cur_year=c(2001,2002,2003,2004))

line = spk_chr(-vec_line[,rank],
        type="line",
        chartRangeMin = min(-vec_line[,rank]),
        chartRangeMax = max(-vec_line[,rank]),
        xvalues = vec_line[,cur_year],
        tooltipFormat= sprintf('<span style=\"color: {{color}}\">&#9679;</span> Year {{x}}: {{y}}.'),
        numberDigitGroupSep = "",
        width = 150,
        height = 50,
        lineColor = '#896B84',
        fillColor = NULL,
        lineWidth = 2)

datatable(data.table(graph = line),
          escape = F,
          options = list(fnDrawCallback = htmlwidgets::JS('function(){HTMLWidgets.staticRender();}')))%>% 
  spk_add_deps()