R: Labels not displaying at a ggplot2 graph - r

Question

Given this R script:
library(glue)
library(ggplot2)
ir.data <- read.csv(file="~/apps/mine/cajueiro_weather_station/sensor_data/temperature_data.csv", header = F)
ir.data$V1 <- as.POSIXct(ir.data$V1, format = "%Y-%m-%dT%H:%M:%S", tz = "UTC")
ir.data$size <- (ir.data$V2 - ir.data$V3)
ggplot(ir.data, aes(x=V1)) +
labs(title = "IR-radiation-based sky temperature monitoring.",
subtitle = glue("Samples from {ir.data$V1[1]}h to {tail(ir.data$V1, n=1)}h UTC-3."),
caption = "Cajueiro Weather Station - fschuindt.githhub.io/blog/weather") +
geom_line(aes(y = V2), color = "#6163c2") +
geom_line(aes(y = V3), color = "#ad1fa2") +
scale_color_discrete(name = "Labels", labels = c("Ambient temperature.", "Sky temperature.")) +
xlab("Timestamp") +
ylab("Measured temperature in °Celcius")
And this .csv data sample:
2022-04-30T19:47:00,28.03,28.05
2022-04-30T19:47:02,27.99,28.01
2022-04-30T19:47:04,28.07,28.01
2022-04-30T19:47:06,28.05,28.05
2022-04-30T19:47:08,28.05,28.01
2022-04-30T19:47:10,28.03,28.01
2022-04-30T19:47:12,28.05,27.99
2022-04-30T19:47:14,28.07,28.01
2022-04-30T19:47:16,28.07,28.05
2022-04-30T19:47:18,28.05,28.05
2022-04-30T19:47:20,28.09,28.07
That's the plot output (the .csv data is bigger than the example):
Why the labels described at scale_color_discrete(name = "Labels", labels = c("Ambient temperature.", "Sky temperature.")) are not being displayed?

Answer 1

It's not recognising those values in an aes call to colour. Reshape data to put all y values in a single column, pass a grouping variable to aes(colour = ...) and use scale_colour_manual to set colours instead:
library(tidyverse)
ir.data <- read_csv(
"2022-04-30T19:47:00,28.03,28.05
2022-04-30T19:47:02,27.99,28.01
2022-04-30T19:47:04,28.07,28.01
2022-04-30T19:47:06,28.05,28.05
2022-04-30T19:47:08,28.05,28.01
2022-04-30T19:47:10,28.03,28.01
2022-04-30T19:47:12,28.05,27.99
2022-04-30T19:47:14,28.07,28.01
2022-04-30T19:47:16,28.07,28.05
2022-04-30T19:47:18,28.05,28.05
2022-04-30T19:47:20,28.09,28.07",
col_names = c("V1", "V2", "V3")
)
ir.data %>%
pivot_longer(-V1, names_to = "Labels", values_to = "V") %>%
ggplot(aes(x = V1, y = V, colour = Labels)) +
labs(
title = "IR-radiation-based sky temperature monitoring.",
subtitle = glue::glue(
"Samples from {ir.data$V1[1]}h to {tail(ir.data$V1, n=1)}h UTC-3."
),
caption = "Cajueiro Weather Station - fschuindt.githhub.io/blog/weather"
) +
geom_line(size = 1) +
scale_color_manual(
name = "Labels",
,
values = c("#6163c2", "#ad1fa2"),
limits = c("V2", "V3"),
labels = c("Ambient temperature.", "Sky temperature."),
) +
xlab("Timestamp") +
ylab("Measured temperature in °Celcius")
Created on 2022-05-06 by the reprex package (v2.0.1)