How to use growth rates with apply function instead of a loop in R

Question

Suppose I have a data frame 'country' with 3 colums:

• year (ranging from 2000 to 2017)
• GDP
• Population

My objective is to grow the GDP and population for the next five years according to assumptions. I have developped the following loop:

country[19:23,1] <- seq(2018, by=1, length.out = 5) 

for (i in 19:nrow(country)){
  country[i,"GDP"] <- country[i-1, "GDP"] * (1 + hypo_gdp/100)
  country[i,"Population"] <- country[i-1, "Population"] * (1 + hypo_pop/100)
}

Where hypo_gdp and hypo_pop are my growth assumptions.

Is there a way to use one of the apply() functions in this case?

Thanks in advance!

Answer 1

You do not need any apply() function in this case. This is just a simple geometric progression:

# simulate some data
country <- data.frame(year = 2000:2017, 
                      GDP = rep(100, 18), 
                      Population = rep(1000, 18))

country[19:23,1] <- seq(2018, by=1, length.out = 5) 

# define gdp and pop parameters
hypo_gdp = 5
hypo_pop = 2

# define common ratios
b1 <- (1 + hypo_gdp/100)
b2 <- (1 + hypo_pop/100)

# calculate values for years 2018-2022
country[19:23,2] =  country$GDP[18]* b1 ^ (1:5)
country[19:23,3] =  country$Population[18]* b2 ^ (1:5)
tail(country)
#    year      GDP Population
# 18 2017 100.0000   1000.000
# 19 2018 105.0000   1020.000
# 20 2019 110.2500   1040.400
# 21 2020 115.7625   1061.208
# 22 2021 121.5506   1082.432
# 23 2022 127.6282   1104.081