How to form contour 2d using 3 arrays list x,y (x,y are positions) and velocity (u)

Question

example of grid

datasets 1 to 50000

data inside dataset

Good morning everyone,

i have attached my photo how it looks please have a look enter image description hereI managed to form a mesh grid. but plotting contour I have a problem.

I have 50000 data sets, each dataset represent a point on the x-axis let's say 1 to 50000. For points on the y-axis, let's say points [(x1, y1), (x1, y2), (x1, y3),........., (x2, y1), (x2, y2)........] On each data sets, I have 2 columns y points and Velocity (u) values on each corresponding y point. that means I have now x,y and u. by using x and y I formed a mesh grid. Now to form velocity contour using u values on each data set to corresponding y values I need to plot contour. that means depending on u values the colour should change from blue to red (Blue is min and red is max, between any rainbow colour) I am confused with logic. I tried different types got a different error every time. Can anyone explain me or try to solve this clearly? I have just started python. please. this is my thesis and important.