Python (twinx plot) Wacky graph

Question

Edit: The graph is fixed now but I am having troubles plotting the legend. It only shows legend for 1 of the plots. As seen in the picture below

I am trying to plot a double axis graph with twinx but I am facing some difficulties as seen in the picture below.

Any input is welcomed! If you require any additional information, I am happy to provide them to you.

as compared to the original before plotting z-axis.

I am unsure why my graph is like that as initially before plotting my secondary y axis, (the pink line), the closing value graph can be seen perfectly but now it seems cut.

It may be due to my data as provided below.

Link to testing1.csv: https://filebin.net/ou93iqiinss02l0g

Code I have currently:

# read csv into variable
sg_df_merged = pd.read_csv("testing1.csv", parse_dates=[0], index_col=0)

# define figure
fig = plt.figure()

fig, ax5 = plt.subplots()
ax6 = ax5.twinx()

x = sg_df_merged.index
y = sg_df_merged["Adj Close"]
z = sg_df_merged["Singapore"]

curve1 = ax5.plot(x, y, label="Singapore", color = "c")
curve2 = ax6.plot(x, z, label = "Face Mask Compliance", color = "m")
curves = [curve1, curve2]

# labels for my axis
ax5.set_xlabel("Year")
ax5.set_ylabel("Adjusted Closing Value ($)")
ax6.set_ylabel("% compliance to wearing face mask")
ax5.grid #not sure what this line does actually

# set x-axis values to 45 degree angle
for label in ax5.xaxis.get_ticklabels():
    label.set_rotation(45)
ax5.grid(True, color = "k", linestyle = "-", linewidth = 0.3)

plt.gca().legend(loc='center left', bbox_to_anchor=(1.1, 0.5), title = "Country Index")
plt.show();

Initially, I thought it was due to my excel having entire blank lines but I have since removed the rows which can be found here

Also, I have tried to interpolate but somehow it doesn't work. Any suggestions on this is very much welcomed

Please see the updates to the answer. I've added a fix for the legend to include labels for both axes, added markers, to make it clear where the data points are, and updated the code for implementing the xtick rotation. — Trenton McKinney, Sep 16 '20 at 20:24
@TrentonMcKinney Wow I really appreciate all your help! Would gladly take you out to coffee if you ever come to Singapore after the pademic ends! — HOA, Sep 16 '20 at 21:07
Thanks. Add me on LinkedIn or Twitter. I'll hold you to that if I'm in your neck of the woods. My contact info is in my SO profile. — Trenton McKinney, Sep 16 '20 at 21:09

Trenton McKinney · Accepted Answer · 2020-09-16T20:22:32.620

Only rows that where all NaN, were dropped. There’s still a lot of rows with NaN.
In order for matplotlib to draw connecting lines between two data points, the points must be consecutive.
The plot API isn't connecting the data between the NaN values
This can be dealt with by converting the pandas.Series to a DataFrame, and using .dropna.
See that x has been dropped, because it will not match the index length of y or z. They are shorter after .dropna.
y is now a separate dataframe, where .dropna is used.
z is also a separate dataframe, where .dropna is used.
The x-axis for the plot are the respective indices.

# read csv into variable
sg_df_merged = pd.read_csv("test.csv", parse_dates=[0], index_col=0)

# define figure
fig, ax5 = plt.subplots(figsize=(8, 6))
ax6 = ax5.twinx()

# select specific columns to plot and drop additional NaN
y = pd.DataFrame(sg_df_merged["Adj Close"]).dropna()
z = pd.DataFrame(sg_df_merged["Singapore"]).dropna()

# add plots with markers
curve1 = ax5.plot(y.index, 'Adj Close', data=y, label="Singapore", color = "c", marker='o')
curve2 = ax6.plot(z.index, 'Singapore', data=z, label = "Face Mask Compliance", color = "m", marker='o')

# labels for my axis
ax5.set_xlabel("Year")
ax5.set_ylabel("Adjusted Closing Value ($)")
ax6.set_ylabel("% compliance to wearing face mask")
    
# rotate xticks
ax5.xaxis.set_tick_params(rotation=45)

# add a grid to ax5
ax5.grid(True, color = "k", linestyle = "-", linewidth = 0.3)

# create a legend for both axes
curves = curve1 + curve2
labels = [l.get_label() for l in curves]
ax5.legend(curves, labels, loc='center left', bbox_to_anchor=(1.1, 0.5), title = "Country Index")

plt.show()

Python (twinx plot) Wacky graph

1 Answers1