Visualizing Time Series
This tutorial focuses on,
plot_time_series(), a workhorse time-series plotting function that:
- Generates interactive
plotlyplots (great for exploring & shiny apps)
- Consolidates 20+ lines of
- Scales well to many time series
- Can be converted from interactive
Run the following code to setup for this tutorial.
Let’s start with a popular time series,
taylor_30_min, which includes energy demand in megawatts at a sampling interval of 30-minutes. This is a single time series.
taylor_30_min #> # A tibble: 4,032 × 2 #> date value #> <dttm> <dbl> #> 1 2000-06-05 00:00:00 22262 #> 2 2000-06-05 00:30:00 21756 #> 3 2000-06-05 01:00:00 22247 #> 4 2000-06-05 01:30:00 22759 #> 5 2000-06-05 02:00:00 22549 #> 6 2000-06-05 02:30:00 22313 #> 7 2000-06-05 03:00:00 22128 #> 8 2000-06-05 03:30:00 21860 #> 9 2000-06-05 04:00:00 21751 #> 10 2000-06-05 04:30:00 21336 #> # … with 4,022 more rows
plot_time_series() function generates an interactive
plotly chart by default.
- Simply provide the date variable (time-based column,
.date_var) and the numeric variable (
.value) that changes over time as the first 2 arguments
.interactive = TRUE, the
.plotly_slider = TRUEadds a date slider to the bottom of the chart.
Next, let’s move on to a dataset with time series groups,
m4_daily, which is a sample of 4 time series from the M4 competition that are sampled at a daily frequency.
m4_daily %>% group_by(id) #> # A tibble: 9,743 × 3 #> # Groups: id  #> id date value #> <fct> <date> <dbl> #> 1 D10 2014-07-03 2076. #> 2 D10 2014-07-04 2073. #> 3 D10 2014-07-05 2049. #> 4 D10 2014-07-06 2049. #> 5 D10 2014-07-07 2006. #> 6 D10 2014-07-08 2018. #> 7 D10 2014-07-09 2019. #> 8 D10 2014-07-10 2007. #> 9 D10 2014-07-11 2010 #> 10 D10 2014-07-12 2002. #> # … with 9,733 more rows
- Groups can be added in 2 ways: by
group_by()or by using the
...to add groups.
- Groups are then converted to facets.
.facet_ncol = 2returns a 2-column faceted plot
.facet_scales = "free"allows the x and y-axis of each plot to scale independently of the other plots
m4_daily %>% group_by(id) %>% plot_time_series(date, value, .facet_ncol = 2, .facet_scales = "free", .interactive = interactive)
Let’s switch to an hourly dataset with multiple groups. We can showcase:
- Log transformation to the
- Use of
.color_varto highlight sub-groups.
m4_hourly %>% group_by(id) #> # A tibble: 3,060 × 3 #> # Groups: id  #> id date value #> <fct> <dttm> <dbl> #> 1 H10 2015-07-01 12:00:00 513 #> 2 H10 2015-07-01 13:00:00 512 #> 3 H10 2015-07-01 14:00:00 506 #> 4 H10 2015-07-01 15:00:00 500 #> 5 H10 2015-07-01 16:00:00 490 #> 6 H10 2015-07-01 17:00:00 484 #> 7 H10 2015-07-01 18:00:00 467 #> 8 H10 2015-07-01 19:00:00 446 #> 9 H10 2015-07-01 20:00:00 434 #> 10 H10 2015-07-01 21:00:00 422 #> # … with 3,050 more rows
The intent is to showcase the groups in faceted plots, but to highlight weekly windows (sub-groups) within the data while simultaneously doing a
log() transformation to the value. This is simple to do:
.value = log(value)Applies the Log Transformation
.color_var = week(date)The date column is transformed to a
lubridate::week()number. The color is applied to each of the week numbers.
All of the visualizations can be converted from interactive
plotly (great for exploring and shiny apps) to static
ggplot2 visualizations (great for reports).
taylor_30_min %>% plot_time_series(date, value, .color_var = month(date, label = TRUE), # Returns static ggplot .interactive = FALSE, # Customization .title = "Taylor's MegaWatt Data", .x_lab = "Date (30-min intervals)", .y_lab = "Energy Demand (MW)", .color_lab = "Month") + scale_y_continuous(labels = scales::comma_format())
plot_time_series_boxplot() function can be used to make box plots.
- Box plots use an aggregation, which is a key parameter defined by the
m4_monthly %>% group_by(id) %>% plot_time_series_boxplot( date, value, .period = "1 year", .facet_ncol = 2, .interactive = FALSE)
A time series regression plot,
plot_time_series_regression(), can be useful to quickly assess key features that are correlated to a time series.
- Internally the function passes a
- A linear regression summary can be output by toggling
show_summary = TRUE.
m4_monthly %>% group_by(id) %>% plot_time_series_regression( .date_var = date, .formula = log(value) ~ as.numeric(date) + month(date, label = TRUE), .facet_ncol = 2, .interactive = FALSE, .show_summary = FALSE )
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