Sort and PlotMATLAB数据从Python

This example shows how to sort data about patients into lists of smokers and nonsmokers in Python^®and plot blood pressure readings for the patients with MATLAB^®.

Start the engine, and read data about a set of patients into a MATLAB table. MATLAB provides a sample comma-delimited file,patients.dat, which contains information on 100 different patients.

import matlab.engine eng = matlab.engine.start_matlab() eng.eval("T = readtable('patients.dat');",nargout=0)

The MATLABreadtablefunction reads the data into a table. The engine does not support the MATLAB table data type. However, with the MATLABtable2structfunction you can convert the table to a scalar structure, which is a data type the engine does support.

eng.eval("S = table2struct(T,'ToScalar',true);",nargout=0) eng.eval("disp(S)",nargout=0)

LastName: {100x1 cell} Gender: {100x1 cell} Age: [100x1 double] Location: {100x1 cell} Height: [100x1 double] Weight: [100x1 double] Smoker: [100x1 double] Systolic: [100x1 double] Diastolic: [100x1 double] SelfAssessedHealthStatus: {100x1 cell}

You can passSfrom the MATLAB workspace into your Python session. The engine convertsSto a Python dictionary,D.

D = eng.workspace["S"]

Shas fields that contain arrays. The engine converts cell arrays to Pythonlistvariables, and numeric arrays to MATLAB arrays. Therefore,D["LastName"]is of data typelist, andD["Age"]is of data typematlab.double.

Sort blood pressure readings into lists of smokers and nonsmokers. Inpatients.dat,columnSmokerindicated a smoker with logical 1 (true), and a nonsmoker with a logical 0 (false). ConvertD["Smoker"]to amatlab.logicalarray for sorting.

smoker = matlab.logical(D["Smoker"])

Convert theDiastolicblood pressure readings andSmokerindicators into 1-by-100 MATLAB arrays for sorting.

pressure = D["Diastolic"] pressure.reshape((1,100)) pressure = pressure[0] smoker.reshape((1,100)) smoker = smoker[0]

Sort thepressurearray into lists of blood pressure readings for smokers and non-smokers. Python list comprehensions provide a compact method for iterating over sequences. With the Pythonzipfunction, you can iterate over multiple sequences in a singleforloop.

sp = [p for (p,s) in zip(pressure,smoker) if s is True] nsp = [p for (p,s) in zip(pressure,smoker) if s is False]

Display the length ofsp,blood pressure readings for smokers in alist.

print(len(sp))

34

Display the length ofnsp,listof readings for nonsmokers.

print (len (nsp))

66

Calculate the mean blood pressure readings for smokers and nonsmokers. Convertspandnspto MATLAB arrays before passing them to the MATLABmeanfunction.

sp = matlab.double(sp) nsp = matlab.double(nsp) print(eng.mean(sp))

89.9117647059

Display the mean blood pressure for the nonsmokers.

print(eng.mean(nsp))

79.3787878788

Plot blood pressure readings for the smokers and nonsmokers. To define twox-axes for plotting, call the MATLABlinspacefunction. You can plot the 34 smokers and 66 nonsmokers on the same scatter plot.

sdx = eng.linspace(1.0,34.0,34) nsdx = eng.linspace(1.0,34.0,66)

Show the axes boundaries with theboxfunction.

eng.figure(nargout=0) eng.hold("on",nargout=0) eng.box("on",nargout=0)

You must call thefigure,hold, andboxfunctions withnargout=0, because these functions do not return output arguments.

Plot the blood pressure readings for the smokers and nonsmokers, and label the plot. For many MATLAB functions, the engine can return a handle to a MATLAB graphics object. You can store a handle to a MATLAB object in a Python variable, but you cannot manipulate the object properties in Python. You can pass MATLAB objects as input arguments to other MATLAB functions.

eng.scatter(sdx,sp,10,'blue')

In the rest of this example, assign the output argument of MATLAB functions tohas a placeholder.

h = eng.scatter (nsdx nsp 10,“红色”)h = eng.xlabel ("Patient (Anonymized)") h = eng.ylabel("Diastolic Blood Pressure (mm Hg)") h = eng.title("Blood Pressure Readings for All Patients") h = eng.legend("Smokers","Nonsmokers")

Draw lines showing the average blood pressure readings for smokers and nonsmokers.

x = matlab.double([0,35]) y = matlab.double([89.9,89.9]) h = eng.line(x,y,"Color","blue") h = eng.text(21.0,88.5,"89.9 (Smoker avg.)","Color","blue") y = matlab.double([79.4,79.4]) h = eng.line(x,y,"Color","red") h = eng.text(5.0,81.0,"79.4 (Nonsmoker avg.)","Color","red")

See Also

readtable|scatter