CODEWITHSUNDEEP
r
thisisourconcerndude
thisisourconcerndude

Reputation: 115

Plotting piecewise functions in R

I'm trying to plot the piecewise function below using if statements, and I keep getting the

Error: unexpected '}' in "}"

message. All of my braces seem just fine to me, so I don't know where this is coming from. Any advice here would be appreciated. (Also, this is basically the first time I've done something like this in R, so please bear with me).

x.values = seq(-2, 2, by = 0.1)
n = length(x.values)
y.values = rep(0, n)
for (i in 1:n) {
x = x.values[i]
if (x <= 0) {
    y.values = -x^3
} else if (x <= 1) {
    y.values = x^2
} else {
    y.values = sqrt(x)
}   y.values[i] = y }

Upvotes: 0

Views: 884

Answers (2)

lebelinoz
lebelinoz

Reputation: 5068

When I ensure the newlines are in the right place, I don't get errors about unexpected symbols:

x.values = seq(-2, 2, by = 0.1)
n = length(x.values)
y.values = rep(0, n)
for (i in 1:n) {
  x = x.values[i]
  if (x <= 0) {
    y.values = -x^3
  } else if (x <= 1) {
    y.values = x^2
  } else {
    y.values = sqrt(x)
  }   
  y.values[i] = y 
}

However, what I do get is a complaint that y doesn't exist on the last line.

Since this is a homework assignment, I'll stop with this partial answer :P

Upvotes: 1

eipi10
eipi10

Reputation: 93811

This can be done without a loop by taking advantage of the fact that R functions are usually vectorized.

For example:

library(tidyverse)
theme_set(theme_classic())

dat = data.frame(x=x.values)

In base R, you can do:

dat$y = with(dat, ifelse(x <= 0, -x^3, ifelse(x<=1, x^2, sqrt(x))))

With tidyverse functions you can do:

dat = dat %>% 
  mutate(y = case_when(x <= 0 ~ -x^3,
                       x <= 1 ~ x^2,
                       TRUE ~ sqrt(x)))

Then, to plot:

ggplot(dat, aes(x,y)) + geom_line() + geom_point()

enter image description here

Upvotes: 2

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