NCL_bar_1.py

This script illustrates the following concepts:

• Drawing bars instead of curves in an XY plot

• Changing the aspect ratio of a bar plot

• Drawing bars up or down based on a Y reference value

See following URLs to see the reproduced NCL plot & script:

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/bar_1.ncl

• Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/bar_1_1_lg.png, https://www.ncl.ucar.edu/Applications/Images/bar_1_2_lg.png and https://www.ncl.ucar.edu/Applications/Images/bar_1_3_lg.png

Import packages:

import numpy as np
import xarray as xr
import matplotlib.pyplot as plt

import geocat.datafiles as gdf
import geocat.viz as gv

Read in data:

# Open a netCDF data file using xarray default engine and load the data
ds = xr.open_dataset(gdf.get("netcdf_files/soi.nc"))
date = ds.date
dsoik = ds.DSOI_KET

# Dates in the file are represented by year and month (YYYYMM)
# representing them fractionally will make plotting the data easier
# This produces the same results as NCL's yyyymm_to_yyyyfrac() function
num_months = np.shape(date)[0]
date_frac = np.empty_like(date)
for n in np.arange(0, num_months, 1):
    yyyy = int(date[n] / 100)
    mon = (date[n] / 100 - yyyy) * 100
    date_frac[n] = yyyy + (mon - 1) / 12

Plot 1 (Bar chart)

# Generate figure (set its size (width, height) in inches) and axes
plt.figure(1, figsize=(10, 5))
ax = plt.gca()

# Set baseline as the minimum of the array, excluding the invalid values
baseline = np.nanmin(dsoik[::8])

# Create barplot
ax.bar(date_frac[::8],
       dsoik[::8] - baseline,
       align='center',
       edgecolor='grey',
       color='white',
       width=8 / 12,
       linewidth=.5,
       bottom=-1.75)

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax,
                         x_minor_per_major=4,
                         y_minor_per_major=5,
                         labelsize=20)

# Use geocat.viz.util convenience function to set axes parameters
gv.set_axes_limits_and_ticks(ax,
                             yticks=np.arange(-2.0, 2.0, 0.5),
                             xlim=(date_frac[40], date_frac[-16]),
                             xticks=np.linspace(1900, 1980, 5))

# Use geocat.viz.util convenience function to set titles and labels
gv.set_titles_and_labels(ax, maintitle="Bar plot", maintitlefontsize=30)

# Draw plot on the screen
plt.tight_layout()
plt.show()

Plot 2 (Bar chart with outlines)

# Generate figure (set its size (width, height) in inches) and axes
plt.figure(2, figsize=(10, 5))
ax = plt.gca()

# Set offset
offset = (date_frac[::8][1] - date_frac[::8][0]) / 2

# Create barplot with outline
xs = [date_frac[::8][0] - offset]
ys = [0]
for i in range(len(date_frac[::8])):
    xs.append(date_frac[::8][i] - offset)
    xs.append(date_frac[::8][i] + offset)
    ys.append(dsoik[::8][i])
    ys.append(dsoik[::8][i])

xs.append(date_frac[::8][-1] + offset)
ys.append(0)

ax.plot(xs, ys, color="black", linewidth=0.5)

# Color the areas within the barplot to only show the outline
ax.fill_between(xs, 0, ys, color='white')

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax,
                         x_minor_per_major=4,
                         y_minor_per_major=5,
                         labelsize=20)

# Use geocat.viz.util convenience function to set axes parameters
gv.set_axes_limits_and_ticks(ax,
                             yticks=np.arange(-2.0, 2.0, 0.5),
                             xlim=(1880, 2000),
                             xticks=np.linspace(1880, 2000, 7))

# Use geocat.viz.util convenience function to set titles and labels
gv.set_titles_and_labels(ax,
                         maintitle="Bar plot with outlines",
                         maintitlefontsize=30)

# Draw plot on the screen
plt.tight_layout()
plt.show()

Plot 3 (Bar chart with a reference line)

# Generate figure (set its size (width, height) in inches) and axes
plt.figure(3, figsize=(10, 5))
ax = plt.gca()

# Create barplot
ax.bar(date_frac[::8],
       dsoik[::8],
       align='edge',
       edgecolor='black',
       color='white',
       width=8 / 12,
       linewidth=.5)

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax,
                         x_minor_per_major=4,
                         y_minor_per_major=5,
                         labelsize=20)

# Use geocat.viz.util convenience function to set axes parameters
gv.set_axes_limits_and_ticks(ax,
                             yticks=np.arange(-2.0, 2.0, 0.5),
                             xlim=(date_frac[40], date_frac[-16]),
                             xticks=np.linspace(1900, 1980, 5))

# Use geocat.viz.util convenience function to set titles and labels
gv.set_titles_and_labels(ax,
                         maintitle="Bar plot with a reference line",
                         maintitlefontsize=30)

# Show the plot
plt.tight_layout()
plt.show()