I have a dataframe (size: 1008,100). the values of cells are within 0.1 and 1. I would like to visualize it in a surface plot but i cannot really figure out what the x,y and z values are gonna be. I'd like to position the surface plot like the rows(1008) is the aligned with the x axis and the columns(100) is aligned with the y axis.
Any help is much appreciated.
thanks
The x and y you are looking for can be created with meshgrid. A good way to start is to find an example on the matplotlib gallery and make changes from there. As an example:
from mpl_toolkits.mplot3d import Axes3D
import matplotlib.pyplot as plt
import pandas as pd
import numpy as np
# create a data frame with 1008x100 values between 0.1 and 1.0
xs = np.arange(0, 1008)
ys = np.arange(0,100)
zs = np.square(xs[:, np.newaxis]) * np.square(ys[np.newaxis, :])
max_value = np.max(zs)
min_value = np.min(zs)
zs = (zs - min_value) / (max_value - min_value) * 0.9 + 0.1
data = pd.DataFrame(zs)
# create X and Y with np.meshgrid and the 2D data frame
# (reusing the scratch variable xs and ys)
xs = np.arange(data.shape[0]) # [0,1,....,1007]
ys = np.arange(data.shape[1]) # [0,1,...,99]
X, Y = np.meshgrid(xs, ys)
# create a surface plot
fig = plt.figure()
ax = fig.gca(projection='3d')
ax.plot_surface(X, Y, data.T)
( note: i needed to transpose the data with .T, don't know why, sometime it is needed...)
Related
Using Matplotlib, I want to plot a 2D heat map. My data is an n-by-n Numpy array, each with a value between 0 and 1. So for the (i, j) element of this array, I want to plot a square at the (i, j) coordinate in my heat map, whose color is proportional to the element's value in the array.
How can I do this?
The imshow() function with parameters interpolation='nearest' and cmap='hot' should do what you want.
Please review the interpolation parameter details, and see Interpolations for imshow and Image antialiasing.
import matplotlib.pyplot as plt
import numpy as np
a = np.random.random((16, 16))
plt.imshow(a, cmap='hot', interpolation='nearest')
plt.show()
Seaborn is a high-level API for matplotlib, which takes care of a lot of the manual work.
seaborn.heatmap automatically plots a gradient at the side of the chart etc.
import numpy as np
import seaborn as sns
import matplotlib.pylab as plt
uniform_data = np.random.rand(10, 12)
ax = sns.heatmap(uniform_data, linewidth=0.5)
plt.show()
You can even plot upper / lower left / right triangles of square matrices. For example, a correlation matrix, which is square and is symmetric, so plotting all values would be redundant.
corr = np.corrcoef(np.random.randn(10, 200))
mask = np.zeros_like(corr)
mask[np.triu_indices_from(mask)] = True
with sns.axes_style("white"):
ax = sns.heatmap(corr, mask=mask, vmax=.3, square=True, cmap="YlGnBu")
plt.show()
I would use matplotlib's pcolor/pcolormesh function since it allows nonuniform spacing of the data.
Example taken from matplotlib:
import matplotlib.pyplot as plt
import numpy as np
# generate 2 2d grids for the x & y bounds
y, x = np.meshgrid(np.linspace(-3, 3, 100), np.linspace(-3, 3, 100))
z = (1 - x / 2. + x ** 5 + y ** 3) * np.exp(-x ** 2 - y ** 2)
# x and y are bounds, so z should be the value *inside* those bounds.
# Therefore, remove the last value from the z array.
z = z[:-1, :-1]
z_min, z_max = -np.abs(z).max(), np.abs(z).max()
fig, ax = plt.subplots()
c = ax.pcolormesh(x, y, z, cmap='RdBu', vmin=z_min, vmax=z_max)
ax.set_title('pcolormesh')
# set the limits of the plot to the limits of the data
ax.axis([x.min(), x.max(), y.min(), y.max()])
fig.colorbar(c, ax=ax)
plt.show()
For a 2d numpy array, simply use imshow() may help you:
import matplotlib.pyplot as plt
import numpy as np
def heatmap2d(arr: np.ndarray):
plt.imshow(arr, cmap='viridis')
plt.colorbar()
plt.show()
test_array = np.arange(100 * 100).reshape(100, 100)
heatmap2d(test_array)
This code produces a continuous heatmap.
You can choose another built-in colormap from here.
Here's how to do it from a csv:
import numpy as np
import matplotlib.pyplot as plt
from scipy.interpolate import griddata
# Load data from CSV
dat = np.genfromtxt('dat.xyz', delimiter=' ',skip_header=0)
X_dat = dat[:,0]
Y_dat = dat[:,1]
Z_dat = dat[:,2]
# Convert from pandas dataframes to numpy arrays
X, Y, Z, = np.array([]), np.array([]), np.array([])
for i in range(len(X_dat)):
X = np.append(X, X_dat[i])
Y = np.append(Y, Y_dat[i])
Z = np.append(Z, Z_dat[i])
# create x-y points to be used in heatmap
xi = np.linspace(X.min(), X.max(), 1000)
yi = np.linspace(Y.min(), Y.max(), 1000)
# Interpolate for plotting
zi = griddata((X, Y), Z, (xi[None,:], yi[:,None]), method='cubic')
# I control the range of my colorbar by removing data
# outside of my range of interest
zmin = 3
zmax = 12
zi[(zi<zmin) | (zi>zmax)] = None
# Create the contour plot
CS = plt.contourf(xi, yi, zi, 15, cmap=plt.cm.rainbow,
vmax=zmax, vmin=zmin)
plt.colorbar()
plt.show()
where dat.xyz is in the form
x1 y1 z1
x2 y2 z2
...
Use matshow() which is a wrapper around imshow to set useful defaults for displaying a matrix.
a = np.diag(range(15))
plt.matshow(a)
https://matplotlib.org/stable/api/_as_gen/matplotlib.axes.Axes.matshow.html
This is just a convenience function wrapping imshow to set useful defaults for displaying a matrix. In particular:
Set origin='upper'.
Set interpolation='nearest'.
Set aspect='equal'.
Ticks are placed to the left and above.
Ticks are formatted to show integer indices.
Here is a new python package to plot complex heatmaps with different kinds of row/columns annotations in Python: https://github.com/DingWB/PyComplexHeatmap
I'm running into an issue trying to create a color map within a scatterplot. Here's the portion of my code:
import numpy as np
import matplotlib.pyplot as plt
from scipy.stats import gaussian_kde
f, ax = plt.subplots()
xy = np.vstack([x, y])
xy = xy[~np.isnan(xy)]
z = gaussian_kde(xy)(xy)
idx = z.argsort()
x, y, z = x[idx], y[idx], z[idx]
plt.scatter(x, y, c=z, cmap='Reds', alpha=0.5)
x and y are both columns within my panda dataframe and they both do have NaN values. I tried taking out all the NaN values by doing ~np.isnan(xy) to only get actual values since it wasn't allowing me to take infs or NaNs since I believe gaussian_kde() was throwing that error. Also, both columns don't align with each other in terms of where those NaN values are and one column has more NaN values than the other. Both also have the same amount of elements. When I run my code, it just keeps running and I have to stop it. Any ideas what's possibly wrong?
You have to filter the Nans using:
inds = ~np.logical_or(np.isnan(x), np.isnan(y))
x = x[inds]
y = y[inds]
From this example, I think your code should look like:
import numpy as np
import matplotlib.pyplot as plt
from scipy.stats import gaussian_kde
# Generate fake data
x = np.random.normal(size=1000)
y = x * 3 + np.random.normal(size=1000)
# removing nans in both vectors at the same place
inds = ~np.logical_or(np.isnan(x), np.isnan(y))
x = x[inds]
y = y[inds]
# Calculate the point density
xy = np.vstack([x,y])
z = gaussian_kde(xy)(xy)
fig, ax = plt.subplots()
ax.scatter(x, y, c=z, s=100, edgecolor='')
plt.show()
Just keep in mind that if x and y are very large vectors, gaussian_kde can take a long time to run. For a vector length of 50000, it takes about 40.5 sec to run.
Although there are several sources on how to plot 3D surfaces with XYZ format. I have a CSV file from a scanning laser that provides no coordinate information on X and Y, just Z coordinates of a rectangular grid.
The file is 800 x 1600 with just z coordinates. Excel can plot it very easily with surface plot, but is limited by size.
How can I approach this problem?
Screenshot of data format
You just need to create arrays of the X and Y coordinates. We can do this with numpy.meshgrid. In the example below, I set the cell size to 1., but you can easily scale that by changing the cellsize variable.
import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D
import numpy as np
# Create x, y coords
nx, ny = 800, 1600
cellsize = 1.
x = np.arange(0., float(nx), 1.) * cellsize
y = np.arange(0., float(ny), 1.) * cellsize
X, Y = np.meshgrid(x, y)
# dummy data
Z = (X**2 + Y**2) / 1e6
# Create matplotlib Figure and Axes
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
print X.shape, Y.shape, Z.shape
# Plot the surface
ax.plot_surface(X, Y, Z)
ax.set_xlabel('X')
ax.set_ylabel('Y')
ax.set_zlabel('Z')
plt.show()
I faced a similar problem and a reply from #tmdavison turn me on in the right direction. But this answer unclear in the part of retrieving data from the CSV file.
Here is my solution.
import csv
import matplotlib.pyplot as plt
import numpy
def csv_3d(file_name):
"""Draw content of csv file with matplotlib 3D like MS Excel."""
data = [
[float(i.replace(',', '.')) for i in row]
for row in csv.reader(open(file_name), delimiter=';')
]
# matplotlib/numpy magic
x_arr, y_arr = numpy.meshgrid(
numpy.arange(0.0, float(len(data[0])), 1.0), # x: number of columns in csv
numpy.arange(0.0, float(len(data)), 1.0), # y: number of rows in csv
)
z_arr = numpy.array(data) # transform csv data into 2D values numpy array
plt.figure(num=file_name)
axes = plt.axes(projection="3d")
axes.plot_surface(x_arr, y_arr, z_arr)
plt.show()
csv_3d('my.csv')
I want to get 2d and 3d plots as shown below.
The equation of the curve is given.
How can we do so in python?
I know there may be duplicates but at the time of posting
I could not fine any useful posts.
My initial attempt is like this:
# Imports
import numpy as np
import matplotlib.pyplot as plt
# to plot the surface rho = b*cosh(z/b) with rho^2 = r^2 + b^2
z = np.arange(-3, 3, 0.01)
rho = np.cosh(z) # take constant b = 1
plt.plot(rho,z)
plt.show()
Some related links are following:
Rotate around z-axis only in plotly
The 3d-plot should look like this:
Ok so I think you are really asking to revolve a 2d curve around an axis to create a surface. I come from a CAD background so that is how i explain things.
and I am not the greatest at math so forgive any clunky terminology. Unfortunately you have to do the rest of the math to get all the points for the mesh.
Heres your code:
#import for 3d
from mpl_toolkits.mplot3d import Axes3D
import numpy as np
import matplotlib.pyplot as plt
change arange to linspace which captures the endpoint otherwise arange will be missing the 3.0 at the end of the array:
z = np.linspace(-3, 3, 600)
rho = np.cosh(z) # take constant b = 1
since rho is your radius at every z height we need to calculate x,y points around that radius. and before that we have to figure out at what positions on that radius to get x,y co-ordinates:
#steps around circle from 0 to 2*pi(360degrees)
#reshape at the end is to be able to use np.dot properly
revolve_steps = np.linspace(0, np.pi*2, 600).reshape(1,600)
the Trig way of getting points around a circle is:
x = r*cos(theta)
y = r*sin(theta)
for you r is your rho, and theta is revolve_steps
by using np.dot to do matrix multiplication you get a 2d array back where the rows of x's and y's will correspond to the z's
theta = revolve_steps
#convert rho to a column vector
rho_column = rho.reshape(600,1)
x = rho_column.dot(np.cos(theta))
y = rho_column.dot(np.sin(theta))
# expand z into a 2d array that matches dimensions of x and y arrays..
# i used np.meshgrid
zs, rs = np.meshgrid(z, rho)
#plotting
fig, ax = plt.subplots(subplot_kw=dict(projection='3d'))
fig.tight_layout(pad = 0.0)
#transpose zs or you get a helix not a revolve.
# you could add rstride = int or cstride = int kwargs to control the mesh density
ax.plot_surface(x, y, zs.T, color = 'white', shade = False)
#view orientation
ax.elev = 30 #30 degrees for a typical isometric view
ax.azim = 30
#turn off the axes to closely mimic picture in original question
ax.set_axis_off()
plt.show()
#ps 600x600x600 pts takes a bit of time to render
I am not sure if it's been fixed in latest version of matplotlib but the setting the aspect ratio of 3d plots with:
ax.set_aspect('equal')
has not worked very well. you can find solutions at this stack overflow question
Only rotate the axis, in this case x
import numpy as np
import matplotlib.pyplot as plt
import mpl_toolkits.mplot3d.axes3d as axes3d
np.seterr(divide='ignore', invalid='ignore')
fig = plt.figure()
ax = fig.add_subplot(111, projection='3d')
x = np.linspace(-3, 3, 60)
rho = np.cosh(x)
v = np.linspace(0, 2*np.pi, 60)
X, V = np.meshgrid(x, v)
Y = np.cosh(X) * np.cos(V)
Z = np.cosh(X) * np.sin(V)
ax.set_xlabel('eje X')
ax.set_ylabel('eje Y')
ax.set_zlabel('eje Z')
ax.plot_surface(X, Y, Z, cmap='YlGnBu_r')
plt.plot(x, rho, 'or') #Muestra la curva que se va a rotar
plt.show()
The result:
I have a 3d plot made using matplotlib. I now want to fill the vertical space between the drawn line and the x,y axis to highlight the height of the line on the z axis. On a 2d plot this would be done with fill_between but there does not seem to be anything similar for a 3d plot. Can anyone help?
here is my current code
from stravalib import Client
import matplotlib as mpl
import numpy as np
import matplotlib.pyplot as plt
... code to get the data ....
mpl.rcParams['legend.fontsize'] = 10
fig = plt.figure()
ax = fig.gca(projection='3d')
zi = alt
x = df['x'].tolist()
y = df['y'].tolist()
ax.plot(x, y, zi, label='line')
ax.legend()
plt.show()
and the current plot
just to be clear I want a vertical fill to the x,y axis intersection NOT this...
You're right. It seems that there is no equivalent in 3D plot for the 2D plot function fill_between. The solution I propose is to convert your data in 3D polygons. Here is the corresponding code:
import math as mt
import matplotlib.pyplot as pl
import numpy as np
import random as rd
from mpl_toolkits.mplot3d import Axes3D
from mpl_toolkits.mplot3d.art3d import Poly3DCollection
# Parameter (reference height)
h = 0.0
# Code to generate the data
n = 200
alpha = 0.75 * mt.pi
theta = [alpha + 2.0 * mt.pi * (float(k) / float(n)) for k in range(0, n + 1)]
xs = [1.0 * mt.cos(k) for k in theta]
ys = [1.0 * mt.sin(k) for k in theta]
zs = [abs(k - alpha - mt.pi) * rd.random() for k in theta]
# Code to convert data in 3D polygons
v = []
for k in range(0, len(xs) - 1):
x = [xs[k], xs[k+1], xs[k+1], xs[k]]
y = [ys[k], ys[k+1], ys[k+1], ys[k]]
z = [zs[k], zs[k+1], h, h]
#list is necessary in python 3/remove for python 2
v.append(list(zip(x, y, z)))
poly3dCollection = Poly3DCollection(v)
# Code to plot the 3D polygons
fig = pl.figure()
ax = Axes3D(fig)
ax.add_collection3d(poly3dCollection)
ax.set_xlim([min(xs), max(xs)])
ax.set_ylim([min(ys), max(ys)])
ax.set_zlim([min(zs), max(zs)])
ax.set_xlabel("x")
ax.set_ylabel("y")
ax.set_zlabel("z")
pl.show()
It produces the following figure:
I hope this will help you.