How to compute the magnitude of a data file

Question

I have two a two component data file (called RealData) that i am able to load and plot into python using matplotlib using the following code;

x = RealData[:,0]
y = RealData[:,1]
plt.plot(x,y

the first few lines of the data is

1431.11555,-0.02399
1430.15118,-0.02387
1429.18682,-0.02294
1428.22245,-0.02167
1427.25809,-0.02066
1426.29373,-0.02020
1425.32936,-0.02022
1424.36500,-0.02041
1423.40064,-0.02047
1422.43627,-0.02029
1421.47191,-0.01993
1420.50755,-0.01950
1419.54318,-0.01913
1418.57882,-0.01888
.........

I would like to plot the magnitude to the data so that the y component become positive, something like

 |y| = squareRoot((-0.02399)^2 + (-0.02387)^2 + ... ))

I think this would involve some sort of for loop or while loop, however I am not sure how to construct it. any help?