Note
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Plotting datetime charts
PyGMT accepts a variety of datetime objects to plot data and create charts.
Aside from the built-in Python datetime
object, PyGMT supports input using
ISO formatted strings, pandas
, xarray
, as well as numpy
.
These data types can be used to plot specific points as well as get
passed into the region
parameter to create a range of the data on an axis.
The following examples will demonstrate how to create plots using the different datetime objects.
import datetime
import numpy as np
import pandas as pd
import pygmt
import xarray as xr
Using Python’s datetime
In this example, Python’s built-in datetime
module is used
to create data points stored in list x
. Additionally,
dates are passed into the region
parameter in the format
(x_start, x_end, y_start, y_end)
,
where the date range is plotted on the x-axis.
An additional notable parameter is style
, where it’s specified
that data points are to be plotted in an X shape with a size
of 0.3 centimeters.
x = [
datetime.date(2010, 6, 1),
datetime.date(2011, 6, 1),
datetime.date(2012, 6, 1),
datetime.date(2013, 6, 1),
]
y = [1, 2, 3, 5]
fig = pygmt.Figure()
fig.plot(
projection="X10c/5c",
region=[datetime.date(2010, 1, 1), datetime.date(2014, 12, 1), 0, 6],
frame=["WSen", "afg"],
x=x,
y=y,
style="x0.3c",
pen="1p",
)
fig.show()
Out:
<IPython.core.display.Image object>
In addition to specifying the date, datetime
supports the exact time at
which the data points were recorded. Using datetime.datetime
the
region
parameter as well as data points can be created with both date and
time information.
Some notable differences to the previous example include
Modifying
frame
to only include West (left) and South (bottom) borders, and removing grid linesUsing circles to plot data points defined through
c
instyle
parameter
x = [
datetime.datetime(2021, 1, 1, 3, 45, 1),
datetime.datetime(2021, 1, 1, 6, 15, 1),
datetime.datetime(2021, 1, 1, 13, 30, 1),
datetime.datetime(2021, 1, 1, 20, 30, 1),
]
y = [5, 3, 1, 2]
fig = pygmt.Figure()
fig.plot(
projection="X10c/5c",
region=[
datetime.datetime(2021, 1, 1, 0, 0, 0),
datetime.datetime(2021, 1, 2, 0, 0, 0),
0,
6,
],
frame=["WS", "af"],
x=x,
y=y,
style="c0.4c",
pen="1p",
color="blue",
)
fig.show()
Out:
<IPython.core.display.Image object>
Using ISO Format
In addition to Python’s datetime
library, PyGMT also supports passing
times in ISO format. Basic ISO strings are formatted as YYYY-MM-DD
with
each -
delineated section marking the four digit year value, two digit
month value, and two digit day value respectively.
When including time of day into ISO strings, the T
character is used, as
can be seen in the following example. This character is immediately followed
by a string formatted as hh:mm:ss
where each :
delineated section
marking the two digit hour value, two digit minute value, and two digit
second value respectively. The figure in the following example is plotted
over a horizontal range of one year from 1/1/2016 to 1/1/2017.
Out:
<IPython.core.display.Image object>
Mixing and matching Python datetime
and ISO dates
The following example provides context on how both datetime
and ISO date
data can be plotted using PyGMT. This can be helpful when dates and times are
coming from different sources, meaning conversions do not need to take place
between ISO and datetime in order to create valid plots.
x = ["2020-02-01", "2020-06-04", "2020-10-04", datetime.datetime(2021, 1, 15)]
y = [1.3, 2.2, 4.1, 3]
fig = pygmt.Figure()
fig.plot(
projection="X10c/5c",
region=[datetime.datetime(2020, 1, 1), datetime.datetime(2021, 3, 1), 0, 6],
frame=["WSen", "afg"],
x=x,
y=y,
style="i0.4c",
pen="1p",
color="yellow",
)
fig.show()
Out:
<IPython.core.display.Image object>
Using pandas.date_range
In the following example, pandas.date_range
produces a list of
pandas.DatetimeIndex
objects, which gets is used to pass date
data to the PyGMT figure.
Specifically x
contains 7 different pandas.DatetimeIndex
objects, with the number being manipulated by the periods
parameter. Each
period begins at the start of a business quarter as denoted by BQS when
passed to the periods
parameter. The initial date is the first argument
that is passed to pandas.date_range
and it marks the first data point
in the list x
that will be plotted.
x = pd.date_range("2018-03-01", periods=7, freq="BQS")
y = [4, 5, 6, 8, 6, 3, 5]
fig = pygmt.Figure()
fig.plot(
projection="X10c/10c",
region=[datetime.datetime(2017, 12, 31), datetime.datetime(2019, 12, 31), 0, 10],
frame=["WSen", "ag"],
x=x,
y=y,
style="i0.4c",
pen="1p",
color="purple",
)
fig.show()
Out:
<IPython.core.display.Image object>
Using xarray.DataArray
In this example, instead of using a pandas.date_range
, x
is
initialized as a list of xarray.DataArray
objects. This object
provides a wrapper around regular PyData formats. It also allows the data to
have labeled dimensions while supporting operations that use various pieces
of metadata.The following code uses pandas.date_range
object to fill
the DataArray with data, but this is not essential for the creation of a
valid DataArray.
x = xr.DataArray(data=pd.date_range(start="2020-01-01", periods=4, freq="Q"))
y = [4, 7, 5, 6]
fig = pygmt.Figure()
fig.plot(
projection="X10c/10c",
region=[datetime.datetime(2020, 1, 1), datetime.datetime(2021, 4, 1), 0, 10],
frame=["WSen", "ag"],
x=x,
y=y,
style="n0.4c",
pen="1p",
color="red",
)
fig.show()
Out:
<IPython.core.display.Image object>
Using numpy.datetime64
In this example, instead of using a pd.date_range
, x
is
initialized as an np.array
object. Similar to xarray.DataArray
this wraps the dataset before passing it as a parameter. However,
np.array
objects use less memory and allow developers to specify
datatypes.
x = np.array(["2010-06-01", "2011-06-01T12", "2012-01-01T12:34:56"], dtype="datetime64")
y = [2, 7, 5]
fig = pygmt.Figure()
fig.plot(
projection="X10c/10c",
region=[datetime.datetime(2010, 1, 1), datetime.datetime(2012, 6, 1), 0, 10],
frame=["WS", "ag"],
x=x,
y=y,
style="s0.5c",
pen="1p",
color="blue",
)
fig.show()
Out:
<IPython.core.display.Image object>
Generating an automatic region
Another way of creating charts involving datetime data can be done
by automatically generating the region of the plot. This can be done
by passing the dataframe to pygmt.info
, which will find
maximum and minimum values for each column and create a list
that could be passed as region. Additionally, the spacing
argument
can be passed to increase the range past the maximum and minimum
data points.
data = [
["20200712", 1000],
["20200714", 1235],
["20200716", 1336],
["20200719", 1176],
["20200721", 1573],
["20200724", 1893],
["20200729", 1634],
]
df = pd.DataFrame(data, columns=["Date", "Score"])
df.Date = pd.to_datetime(df["Date"], format="%Y%m%d")
fig = pygmt.Figure()
region = pygmt.info(
table=df[["Date", "Score"]], per_column=True, spacing=(700, 700), coltypes="T"
)
fig.plot(
region=region,
projection="X15c/10c",
frame=["WSen", "afg"],
x=df.Date,
y=df.Score,
style="c0.4c",
pen="1p",
color="green3",
)
fig.show()
Out:
<IPython.core.display.Image object>
Setting Primary and Secondary Time Axes
This example focuses on labeling the axes and setting intervals
at which the labels are expected to appear. All of these modifications
are added to the frame
parameter and each item in that list modifies
a specific section of the plot.
Starting off with WS
, adding this string means that only
Western/Left (W) and Southern/Bottom (S) borders of
the plot will be shown. For more information on this, please
refer to frame instructions.
The other important item in the frame
list is
"sxa1Of1D"
. This string modifies the secondary
labeling (s) of the x-axis (x). Specifically,
it sets the main annotation and major tick spacing interval
to one month (a1O) (capital letter o, not zero). Additionally,
it sets the minor tick spacing interval to 1 day (f1D).
The labeling of this axis can be modified by setting
FORMAT_DATE_MAP to ‘o’ to use the month’s
name instead of its number. More information about configuring
date formats can be found on the
official GMT documentation page.
x = pd.date_range("2013-05-02", periods=10, freq="2D")
y = [4, 5, 6, 8, 9, 5, 8, 9, 4, 2]
fig = pygmt.Figure()
with pygmt.config(FORMAT_DATE_MAP="o"):
fig.plot(
projection="X15c/10c",
region=[datetime.datetime(2013, 5, 1), datetime.datetime(2013, 5, 25), 0, 10],
frame=["WS", "sxa1Of1D", "pxa5d", "sy+lLength", "pya1+ucm"],
x=x,
y=y,
style="c0.4c",
pen="1p",
color="green3",
)
fig.show()
Out:
<IPython.core.display.Image object>
The same concept shown above can be applied to smaller as well as larger intervals. In this example, data is plotted for different times throughout two days. Primary x-axis labels are modified to repeat every 6 hours and secondary x-axis label repeats every day and shows the day of the week.
Another notable mention in this example is setting FORMAT_CLOCK_MAP to “-hhAM” which specifies the format used for time. In this case, leading zeros are removed using (-), and only hours are displayed. Additionally, an AM/PM system is being used instead of a 24-hour system. More information about configuring time formats can be found on the official GMT documentation page.
x = pd.date_range("2021-04-15", periods=8, freq="6H")
y = [2, 5, 3, 1, 5, 7, 9, 6]
fig = pygmt.Figure()
with pygmt.config(FORMAT_CLOCK_MAP="-hhAM"):
fig.plot(
projection="X15c/10c",
region=[
datetime.datetime(2021, 4, 14, 23, 0, 0),
datetime.datetime(2021, 4, 17),
0,
10,
],
frame=["WS", "sxa1K", "pxa6H", "sy+lSpeed", "pya1+ukm/h"],
x=x,
y=y,
style="n0.4c",
pen="1p",
color="lightseagreen",
)
fig.show()
Out:
<IPython.core.display.Image object>
Total running time of the script: ( 0 minutes 10.516 seconds)