Matplotlib堆积的条形图系列未显示

Question

Why does the second series not always show up, as below?

---

Scenario 1:

score_sim = (70, 80, 90)
score_feat = (10, 20, 30)
ind = np.arange(len(score_sim))
width = 0.35

p1 = plt.bar(ind, score_feat, width)
p2 = plt.bar(ind, score_sim, width)

Gives:

p2 isn't showing?

---

Scenario 2:

score_sim = (70, 80, 90)
score_feat = (100, 200, 300)
ind = np.arange(len(score_sim))
width = 0.35

p1 = plt.bar(ind, score_feat, width)
p2 = plt.bar(ind, score_sim, width)

Gives:

---

---

So, why does only the second one show two series? I want to have the blue series below the green one. How do I do this?

Answer 1

In scenario 1, the bars for score_feat are correctly plotted, but then they are covered by the values for score_sim . plt.bar has an argument bottom that accept a scalar or an array and specifies the vertical starting point of a bar. eg If you want to stack the bars for the two series on scenario 1, use as second plotting command:

p2 = plt.bar(ind, score_sim, width,bottom=score_feat)

Answer 2

In Scenario 1, the bars of the second plot are larger than the bars from the first plot. Hence they overlay the other bars. In scenario 2, the bars of the second plot are smaller than those from the first, hence the bars in the background are still visible.

Note that both plots do not show "stacked" bars; all bars start at y=0.

In order to have a specific plot shown in front of the other the easiest solution is to plot is last, ie in scenario 1

p2 = plt.bar(ind, score_sim, width)
p1 = plt.bar(ind, score_feat, width)

Other than that, you may use zorder to plot one plot in front of the other. The higher the zorder to more in front the plot.

p1 = plt.bar(ind, score_feat, width, zorder=4)
p2 = plt.bar(ind, score_sim, width, zorder=3)
# p1 will be shown in front of p2, even though it is later defined, 
# because it has the larger zorder