ggplot2: Plot of function with different lines for each parameter value

Question

How to plot several different line-cum-point curves based on different parameter values in a formula?

I want to plot a simple formula, say one for compound interest. The x-axis should have years and the y -axis should have final amount. There should be several curves, one for each interest rate on the same set of axes. I am getting just one column containing ALL the values and not several columns, one for each value of the rate.

 r <- c(0,.05,.08,.1,.15)  # Interest rates
 C <- 100                  # Initial amount
 t <- seq(0, 20, by = 1)   # Say, 20 years investment

 fv <- C*(1+r)^t 

 df <- data.frame(cbind(t,fv))  # creates the data frame but with only 2 columns.

 ggplot(df)+               # will obviously not plot several curves
 geom_point(aes(x = t, y = FV), size = 3)+
 geom_line()              # I need a line for each r value
 xlab("Number of years")+
 ylab(paste("Future value of Rupees",C))

Will using the above vectorized approach work? Or do I need a for loop for this?

Answer 1

You can try building the data frame with dplyr and map r to the color aesthetic in ggplot

library(tidyverse)

df <- data.frame(
  r = sort(rep(c(0,.05,.08,.1,.15), 21)),
  t = rep(seq(0, 20, by = 1), 5)
)

df %>%
  dplyr::mutate(fv = 100 * (1 + r)^t) %>%
  ggplot(aes(x = t, y = fv, color = r)) +             
  geom_point(size = 3) +
  xlab("Number of years")+
  ylab(paste("Future value of Rupees", 100))

^{Created on 2019-10-13 by the reprex package (v0.3.0)}