[Python] add colorbar to a sequence of line plots

Discussão em 'Python' iniciado por Stack, Setembro 1, 2025.

  1. Stack

    Stack Membro Participativo

    I have a sequence of line plots for two variables (x,y) for a number of different values of a variable z. I would normally add the line plots with legends like this:

    import matplotlib.pyplot as plt

    fig = plt.figure()
    ax = fig.add_subplot(111)
    # suppose mydata is a list of tuples containing (xs, ys, z)
    # where xs and ys are lists of x's and y's and z is a number.
    legns = []
    for(xs,ys,z) in mydata:
    pl = ax.plot(xs,ys,color = (z,0,0))
    legns.append("z = %f"%(z))
    ax.legends(legns)
    plt.show()


    But I have too many graphs and the legends will cover the graph. I'd rather have a colorbar indicating the value of z corresponding to the color. I can't find anything like that in the galery and all my attempts do deal with the colorbar failed. Apparently I must create a collection of plots before trying to add a colorbar.

    Is there an easy way to do this? Thanks.

    EDIT (clarification):

    I wanted to do something like this:

    import matplotlib.pyplot as plt
    import matplotlib.cm as cm

    fig = plt.figure()
    ax = fig.add_subplot(111)
    mycmap = cm.hot
    # suppose mydata is a list of tuples containing (xs, ys, z)
    # where xs and ys are lists of x's and y's and z is a number between 0 and 1
    plots = []
    for(xs,ys,z) in mydata:
    pl = ax.plot(xs,ys,color = mycmap(z))
    plots.append(pl)
    fig.colorbar(plots)
    plt.show()


    But this won't work according to the Matplotlib reference because a list of plots is not a "mappable", whatever this means.

    I've created an alternative plot function using LineCollection:

    def myplot(ax,xs,ys,zs, cmap):
    plot = lc([zip(x,y) for (x,y) in zip(xs,ys)], cmap = cmap)
    plot.set_array(array(zs))
    x0,x1 = amin(xs),amax(xs)
    y0,y1 = amin(ys),amax(ys)
    ax.add_collection(plot)
    ax.set_xlim(x0,x1)
    ax.set_ylim(y0,y1)
    return plot


    xs and ys are lists of lists of x and y coordinates and zs is a list of the different conditions to colorize each line. It feels a bit like a cludge though... I thought that there would be a more neat way to do this. I like the flexibility of the plt.plot() function.

    Continue reading...

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