Time series from three years in one plot

Question

I am struggling (due to lack of knowledge and experience) to create a plot in R with time series from three different years (2009, 2013 and 2017). Failing to solve this problem by searching online has led me here.

I wish to create a plot that shows change in nitrate concentrations over the course of May to October for all years, but keep failing since the x-axis is defined by one specific year. I also receive errors because the x-axis lengths differ (due to different number of samples). To solve this I have tried making separate columns for month and year, with no success.

Data example:

date        NO3.mg.l     year    month
2009-04-22  1.057495     2009     4
2013-05-08  1.936000     2013     5
2017-05-02  2.608000     2017     5

Code:

ggplot(nitrat.all, aes(x = date, y = NO3.mg.l, colour = year)) + geom_line()

This code produces a plot where the lines are positioned next to one another, whilst I want a plot where they overlay one another. Any help will be much appreciated.

Nitrate plot

Ekatef Ekatef · Accepted Answer · 2018-02-08T10:58:05

Probably, that will be helpful for plotting:

library("lubridate")
library("ggplot2")
# evample of data with some points for each year
nitrat.all <- data.frame(date = c(ymd("2009-03-21"), ymd("2009-04-22"), ymd("2009-05-27"),
    ymd("2010-03-15"), ymd("2010-04-17"), ymd("2010-05-10")), NO3.mg.l = c(1.057495, 1.936000, 2.608000,
        3.157495, 2.336000, 3.908000))
nitrat.all$year <- format(nitrat.all$date, format = "%Y")
ggplot(data = nitrat.all) +
    geom_point(mapping = aes(x = format(date, format = "%m-%d"), y = NO3.mg.l, group = year, colour = year)) +
    geom_line(mapping = aes(x = format(date, format = "%m-%d"), y = NO3.mg.l, group = year, colour = year))

As for selecting of the dates corresponding to a certain month, you may subset your data frame by a condition using basic R-functions:

n_month1 <- 3 # an index of the first month of the period to select
n_month2 <- 4 # an index of the first month of the period to select
test_for_month <- (as.numeric(format(nitrat.all$date, format = "%m")) >= n_month1) & 
    (as.numeric(format(nitrat.all$date, format = "%m")) <= n_month2)
nitrat_to_plot <- nitrat.all[test_for_month, ]

Another quite an elegant approach is to use filter() from dplyr package

nitrat.all$month <- as.numeric(format(nitrat.all$date, format = "%m"))
library("dplyr")
nitrat_to_plot <- filter(nitrat.all, ((month >= n_month1) & (month <= n_month2)))

Time series from three years in one plot

1 Answers