How do I change x-axis from numeric to custom ggplot? - r

Question

I have data that looks like:
require(ggplot2); require(lubridate); require(data.table); require(dplyr)
Date <- rep(seq.Date(as.Date("2014-01-01"), as.Date("2016-12-31"), by = "days"), 3)
Index <- rep(c(rep(1:365, times = 2), 1:366), 3)
Counts<- sample(1:25, size = length(Index), replace = TRUE)
City <- rep(c("Dallas", "San Antonio", "Houston"), each = length(Index)/3)
df <- data.frame(Date = Date, Index = Index, Counts = Counts, City = City)
df <- df %>% mutate(Year = year(as.Date(Date)))
I graphed the data using the following code:
ggplot(df, aes(x = Index, y = Counts, colour = City)) +
geom_line(aes(group = City))+
geom_vline(xintercept = c(31, 59.5, 90, 120, 151, 181, 212, 243, 273, 304, 334))+
facet_grid(Year~.) +
theme(legend.position = "bottom")
My goal is to actually label the x-axis as Jan Feb ... Dec. I have tried scale_x_continuous and scale_x_discrete with no avail. Any suggestions?
Thanks in advance

Answer 1

I think this is easier to achieve if you use Date as your x variable and make use of scale_x_date:
df <- df %>% mutate(Year = year(as.Date(Date)),
MonthStart = round_date(Date, unit = "month"))
mid_months <- seq.Date(as.Date("2014-01-15"), as.Date("2016-12-15"), by = "months")
ggplot(df, aes(x = Date, y = Counts, colour = City)) +
geom_line(aes(group = City))+
facet_wrap(~ Year, ncol = 1, scales = "free") +
geom_vline(aes(xintercept = MonthStart), colour = 'black') +
# expand = c(0,0) to ensure scale doesn't extend to additional
# months
scale_x_date(breaks = mid_months, date_labels = "%b", expand = c(0, 0)) +
theme(legend.position = "bottom")
EDIT: updated to add mid-month labels

Answer 2

A quick option to make use of what you've already got is to pass your vector of x intercepts to scale_x_continuous as breaks, and use month.abb to name them:
library(tidyverse)
df <- data_frame(
Date = rep(seq.Date(as.Date("2014-01-01"), as.Date("2016-12-31"), by = "days"), 3),
Index = rep(c(rep(1:365, times = 2), 1:366), 3),
Counts = sample(1:25, size = length(Index), replace = TRUE),
City = rep(c("Dallas", "San Antonio", "Houston"), each = length(Index) / 3),
Year = lubridate::year(Date)
)
month_breaks <- c(31, 59.5, 90, 120, 151, 181, 212, 243, 273, 304, 334)
ggplot(df, aes(x = Index, y = Counts, colour = City)) +
geom_line() +
geom_vline(xintercept = month_breaks) +
scale_x_continuous(breaks = month_breaks, labels = month.abb[-1]) +
facet_grid(Year ~ .) +
theme(legend.position = "bottom")