axis annotations and text do not show up for specific data inputs

Question

Using matplotlib in python I have the issue, that for specific inputs axis annotation and axis labels are not shown.

I wrote the following code:

df = pd.read_csv(os.path.join(input_path, "data.csv"), sep=",")

category = df.columns[1]
items = df[df.columns[0]]

_, ax = plt.subplots(figsize=(10, 6))

x_coordinates = np.arange(len(items))
ax.plot(
    x_coordinates,
    list(df[category]),
    label=category.title(),
)

ax.set_xlabel(items.name.title())
ax.set_ylabel(category.title())
ax.set_title("Test chart", wrap=True)
ax.set_xticks(x_coordinates, [str(item).title() for item in items])

y_coordinates = list(df[df.columns[1]])
x_coordinates = list(items)

for x_coordinate, y_coordinate in zip(x_coordinates, y_coordinates):
    ax.text(
        x_coordinate - 1,
        y_coordinate,
        y_coordinate,  # This is the text that should be displayed
        dict(zorder=10, size=10, color="black", ha="center"),
    )

plt.savefig("output.png")

Let's look at this input data.csv:

week,attendance
1,74788
2,74884
3,57677
4,74879
5,52632
6,74997
7,74292
8,49699
9,74908
10,74482
11,74379
12,42910
13,74186
14,37886
15,60038

The text/annotations are plotted correctly:

correct annotation

However, given the following input data.csv:

year,purse
2001,60000
2002,60000
2003,60000
2004,70000
2005,70000
2006,85000
2007,100000
2008,100000
2009,110000
2010,120000
2011,120000
2012,100000
2013,100000

The following chart is plotted:

missing annotation

I am observing the same behavior for other data inputs. For some the annotations are displayed, for some not. I can not find a common denominator as to why the issue occurs with the input data. Is there a fault in my code which I am overlooking?

The same issue also occurs using ax.annotate (which also builds on top of ax.text):

    ax.annotate(
        value_label,
        xy=(x_coordinate - 1, y_coordinate),
        textcoords="offset points",
        xytext=(0, 0),
        zorder=10,
    )

I tried debugging the issue, but all the input values to .text/.annotate are correct.

Help would be greatly appreciated!

Tino D · Accepted Answer · 2024-11-10 09:30:54Z

TL;DR the usage of x_coordinates is not right. The first time it worked because the numbers were going from 1->15. Which means that x_coordinates = np.arange(len(items)) would work only if the values are indeed equal to the sample number. If you zoom to x 2000-2014 in your second example, you will find the annotations (check image below).

Additionally, your code has some redundant lines and conversions.

list(df[category]) is not needed
y_coordinates = list(df[df.columns[1]]) and x_coordinates = list(items) are also not needed
I also don't understand the reason behind the usage of category = df.columns[1] and items = df[df.columns[0]]

Here's a more efficient way, do ask anything if something is not clear from the comments:

df = pd.read_csv("data.csv", index_col=0) # set the first column as an index
plt.plot(df) # plot the df with respect to its' index
plt.xlabel(df.index.name) # set xlabel
plt.ylabel(df.columns[0]) # and y label
for x, y in zip(df.index, df.iloc[:,0]): # annotate values, here you can also play arround with skipping rows...
    plt.text(x, y, f"{y}", ha="center", va="bottom", fontsize=10, color="black")

For first dataset:

And the second one:

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