CODEWITHSUNDEEP
pythonmatplotlibgrapherrorbar
Rima
Rima

Reputation: 299

How to format errorbars in matplotlib

I am importing data from a file into a pandas DataFrame and I want to graph that data with errorbars. Here is my code:

y = df['PP04-O3N2SNpos log(O/H)+12'] - df['nuclear metallicity']
yerr = np.array([df['negative error!'],df['positive error!']]).T
x = df['NED calculated virgo infall distance in Kpc']

plt.errorbar(x,y,yerr,fmt = 'r^')
plt.xlabel('Distance from center in kpc')
plt.ylabel('PP04-O3N2SNpos log(O/H)+12')
plt.title('Central metallicity vs SN metallicity')
plt.show()

However, the graph I get looks like this enter image description here

As you can see, the format of the errorbars on the graph is all messed up. I'm not sure why it isn't plotting like normal errorbars, but instead with lines randomly placed.

Upvotes: 2

Views: 1267

Answers (1)

Diziet Asahi
Diziet Asahi

Reputation: 40697

Your problem is with the shape of your yerr array. The documentation says that the array should be a Nx1 array or a 2xN array. Your yerr array has a Nx2 shape.

replace your second line with

# create a 2xN array for the error bars
yerr = np.array([df['negative error!'],df['positive error!']])

and you should be ok

Upvotes: 3

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