[英]matplotlib 2D plot from x,y,z values
I am a Python beginner.我是 Python 初学者。
I have a list of X values我有一个 X 值列表
x_list = [-1,2,10,3]
and I have a list of Y values我有一个 Y 值列表
y_list = [3,-3,4,7]
I then have a Z value for each couple.然后我有每对夫妇的 Z 值。 Schematically, this works like that:
从原理上讲,它是这样工作的:
X Y Z
-1 3 5
2 -3 1
10 4 2.5
3 7 4.5
and the Z values are stored in z_list = [5,1,2.5,4.5]
. Z 值存储在
z_list = [5,1,2.5,4.5]
中。 I need to get a 2D plot with the X values on the X axis, the Y values on the Y axis, and for each couple the Z value, represented by an intensity map.我需要得到一个 2D 图,其中 X 轴上的 X 值、Y 轴上的 Y 值以及由强度图表示的每一对 Z 值。 This is what I have tried, unsuccessfully:
这是我尝试过的,但没有成功:
X, Y = np.meshgrid(x_list, y_list)
fig, ax = plt.subplots()
extent = [x_list.min(), x_list.max(), y_list.min(), y_list.max()]
im=plt.imshow(z_list, extent=extent, aspect = 'auto')
plt.colorbar(im)
plt.show()
How to get this done correctly?如何正确完成这项工作?
The problem is that imshow(z_list, ...)
will expect z_list
to be an (n,m)
type array, basically a grid of values.问题是
imshow(z_list, ...)
会期望z_list
是一个(n,m)
类型的数组,基本上是一个值网格。 To use the imshow function, you need to have Z values for each grid point, which you can accomplish by collecting more data or interpolating.要使用 imshow 函数,您需要为每个网格点设置 Z 值,这可以通过收集更多数据或插值来完成。
Here is an example, using your data with linear interpolation:这是一个示例,使用具有线性插值的数据:
from scipy.interpolate import interp2d
# f will be a function with two arguments (x and y coordinates),
# but those can be array_like structures too, in which case the
# result will be a matrix representing the values in the grid
# specified by those arguments
f = interp2d(x_list,y_list,z_list,kind="linear")
x_coords = np.arange(min(x_list),max(x_list)+1)
y_coords = np.arange(min(y_list),max(y_list)+1)
Z = f(x_coords,y_coords)
fig = plt.imshow(Z,
extent=[min(x_list),max(x_list),min(y_list),max(y_list)],
origin="lower")
# Show the positions of the sample points, just to have some reference
fig.axes.set_autoscale_on(False)
plt.scatter(x_list,y_list,400,facecolors='none')
You can see that it displays the correct values at your sample points (specified by x_list
and y_list
, shown by the semicircles), but it has much bigger variation at other places, due to the nature of the interpolation and the small number of sample points.您可以看到它在您的样本点(由
x_list
和y_list
指定,由半圆显示)显示正确的值,但由于插值的性质和样本点的数量很少,它在其他地方的变化更大.
Here is one way of doing it:这是一种方法:
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.colors import LogNorm
x_list = np.array([-1,2,10,3])
y_list = np.array([3,-3,4,7])
z_list = np.array([5,1,2.5,4.5])
N = int(len(z_list)**.5)
z = z_list.reshape(N, N)
plt.imshow(z, extent=(np.amin(x_list), np.amax(x_list), np.amin(y_list), np.amax(y_list)), norm=LogNorm(), aspect = 'auto')
plt.colorbar()
plt.show()
I followed this link: How to plot a density map in python?我点击了这个链接: 如何在 python 中绘制密度图?
I am not as sharp when it comes to use python and matplotlib, but I wanted to share my experience.在使用 python 和 matplotlib 时我没有那么敏锐,但我想分享我的经验。 My trouble is that my X and Y datasets were not the same length, as well as being relatively heavy datasets, which turned out to be dysfunctional using any of the methods mentioned above.
我的问题是我的 X 和 Y 数据集长度不一样,而且是相对较重的数据集,使用上述任何方法都证明是功能失调的。 Therefore, I used the heavy, inelegant method with a loop to populate the Z matrix.
因此,我使用带有循环的繁重、不雅的方法来填充 Z 矩阵。 It takes 2-3 minutes on my laptop, but it does exactly what I want.
在我的笔记本电脑上需要 2-3 分钟,但它完全符合我的要求。
"""
@author: Benoit
"""
import matplotlib.pyplot as plt
plt.style.use('seaborn-white')
import numpy as np
import matplotlib.cm as cm
data = np.genfromtxt('MY_DATA_FILE.csv', delimiter=';', skip_header = 1)
#list of X, Y and Z
x_list = data[:,0]
y_list = data[:,1]
z_list = data[:,2]
length = np.size(x_list)
#list of X and Y values (np.unique removes redundancies)
N_x = np.unique(x_list)
N_y = np.unique(y_list)
X, Y = np.meshgrid(N_x,N_y)
length_x = np.size(N_x)
length_y = np.size(N_y)
#define empty intensity matrix
Z = np.full((length_x, length_y), 0)
#the f function will chase the Z values corresponding
# to a given x and y value
def f(x, y):
for i in range(0, length):
if (x_list[i] == x) and (y_list[i] == y):
return z_list[i]
#a loop will now populate the Z matrix
for i in range(0, length_x - 1):
for j in range(0, length_y - 1):
Z[i,j] = f(N_x[i], N_y[j])
#and then comes the plot, with the colour-blind-friendly viridis colourmap
plt.contourf(X, Y, np.transpose(Z), 20, origin = 'lower', cmap=cm.viridis, alpha = 1.0);
cbar = plt.colorbar()
cbar.set_label('intensity (a.u.)')
#optional countour lines:
"""contours = plt.contour(X, Y, np.transpose(Z), colors='black');
plt.clabel(contours, inline=True, fontsize=8)
"""
plt.xlabel('X_TITLE (unit)')
plt.ylabel('Y_TITLE (unit)')
plt.axis(aspect='image')
plt.show()
plt.savefig('TYPE_YOUR_NAME.png', DPI = 600)
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