带有自定义刻度的散点图 [英] Scatter plot with custom ticks

问题描述

我想在 y 轴上绘制波长(浮点数)的散点图，在 x 轴上绘制光谱类(字符/字符串列表)，labels = ['B','A','F','G'、'K'、'M'].数据保存在 pandas dataframe, df 中.

I want to do a scatter plot of a wavelength (float) in y-axis and spectral class (list of character/string) in x-axis, labels = ['B','A','F','G','K','M']. Data are saved in pandas dataframe, df.

df['Spec Type Index']
0      NaN
1        A
2        G
.        .
.        .
167      K
168    Nan
169      G

那么，

df['Disk Major Axis "']
0        4.30
1        4.50
2       22.00
.         .
.         .
167      1.32
168      0.28
169     25.00

因此，我认为这应该简单地使用

Thus, I thought this should be done simply with

plt.scatter(df['Spec Type Index'], df['Disk Major Axis "'])

但是我遇到了这个烦人的错误

But I get this annoying error

无法将字符串转换为浮点数:'G'

could not convert string to float: 'G'

解决此问题后，我想按如下方式制作自定义 xticks.但是，我怎么能

After fixing this, I want to make custom xticks as follows. However, how can I

labels = ['B','A','F','G','K','M']
ticks = np.arange(len(labels))
plt.xticks(ticks, labels)

推荐答案

首先，我认为您必须将这些字符串映射到整数，然后 matplotlib 可以决定放置这些点的位置.

First, I think you have to map those strings to integers then matplotlib can decide where to place those points.

labels = ['B','A','F','G','K','M']
mapping = {'B': 0,'A': 1,'F': 2,'G': 3,'K': 4,'M': 5}
df = df.replace({'Spec Type Index': mapping})

然后绘制散点图，

fig, ax = plt.subplots()
ax.scatter(df['Spec Type Index'], df['Disk Major Axis "'])

最后，

ax.set_xticklabels(labels)

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