Visualizing time series

Introduction to Data Visualization with Julia

Gustavo Vieira Suñe

Data Analyst

Time series

A line chart displaying tomato prices as a function of time. The line shows a time series with a positive trend and high variability.

Tomato prices

tomato DataFrame

Date	Price (Rupees)
FEB-2004	10.0
MAR-2004	12.0
APR-2004	6.0
MAY-2004	8.0
...	...

Sort dates

tomato.Date = sort(
  tomato.Date, :Date
)

# Plot time series
plot(
    tomato.Date,
    tomato.Price,

    # Customize the plot
    linewidth=2,
    linecolor=:tomato,
    label="Tomato"
)
xlabel!("Date")
ylabel!("Unit Price (Rupees)")

Tomato prices

A line chart displaying tomato prices as a function of time. The x-axis labels overlap each other.

tomato DataFrame

Date	Price (Rupees)
APR-2004	6.0
APR-2005	10.0
APR-2006	8.0
APR-2007	8.0
...	...

Date column has strings!

Dates with Julia

using Dates

birthday = Date("1989-12-04")

Other formats

birthday = Date(
    "1989/DEC/04", dateformat"y/u/d"
)
birthday = Date(
    "Dec 4, 1989", dateformat"u d, y"
)

Code	Match	Examples
Y/y	Year (YYYY)	1989, 2023
m	Month (MM)	1, 10
u	Abbreviated Month	Jan, DEC
U	Month Name	January, DECEMBER
d	Day (DD)	4, 28
H	Hour (HH)	12, 22
M	Minute (MM)	05, 25
S	Second (SS)	10, 59

¹ https://docs.julialang.org/en/v1/stdlib/Dates/#Period-Types

Tomato prices with Dates

Convert strings to Dates

tomato.Date = Date.(
    tomato.Date, dateformat"u-y"
)

Sort by date

tomato.Date = sort(
    tomato.Date, :Date
)

Date	Price (Rupees)
2004-02-01	10.0
2004-03-01	12.0
2004-04-01	6.0
2004-05-01	8.0
...	...

Tomato price time series

# Plot time series
plot(
    tomato.Date,
    tomato.Price,
    # Customize the plot
    linewidth=2,
    linecolor=:tomato,
    label="Tomato"
)
xlabel!("Date")
ylabel!("Unit Price (Rupees)")

A line chart displaying tomato prices as a function of time. The x-axis labels are formatted as dates and do not overlap each other.

Annotating a plot

# Row with highest price 
maximum_price = tomato[
    argmax(tomato.Price), :]

# Annotate the plot
annotate!(
    # Coordinates
    maximum_price.Date,
    maximum_price.Price + 2,

    # Annotation text
    "Highest Price",
    annotationfontsize=8
)

A line chart displaying tomato prices as a function of time. The point with the highest price is indicated with an annotation.

Let's practice!

Introduction to Data Visualization with Julia