# Chapter 15 Challenge 2

You have realized that your tool for measuring uptake was not calibrated properly at Quebec sites and all measurements are 2 units higher than they should be.

1. Use a loop to correct these measurements for all Québec sites.

2. Use a vectorisation-based method to calculate the mean $$CO_2$$ uptake in both areas.

For this, you must load the $$\text{CO}_{2}$$ dataset using data(CO2), and then use the object CO2.

1.-Using for and if to correct the measurements:

for (i in 1:length(CO2[, 1])) {
if (CO2$Type[i] == "Quebec") { CO2$uptake[i] <- CO2$uptake[i] - 2 } } 2.- Using tapply() to calculate the mean for each group: tapply(CO2$uptake, CO2\$Type, mean)
##      Quebec Mississippi
##    31.54286    20.88333