# How to make the target’s position different from the previous target’s position?

Hello all,
How to make the position variable different from the previous trail? That is, when the participant does the experiment, the position of trail N and trail N-1 are different. I don’t want to use the method of generating excel tables, I want to realize this randomization in psychopy, where should I add this code?I appreciate your help.

Hello,
Here is a possible solution using the `random` library. This solution will only work for offline experiments but should also be easy to implement for online experiments.

``````# Start Experiment
import random

def randomLocation():
return round(random.uniform(-1, 1), 3)

# Start Routine
currentLocation = [randomLocation(), randomLocation()]
``````

Then, set the position to change on every repeat and set it to `\$currentLocation`.

You might need to reduce the range from -1 → 1, to -0.8 → 0.8, depending on your stimulus size.

Chen

Thank you very much!!
But with a little tweaking in the coder,
Put currentLocation = [randomLocation(), randomLocation()] before polygon.setPos()

The way I approach this kind of issue, to avoid random locations being too close to previous random locations, is to create a grid of jittered points and then shuffle them.

I’ve just updated my points on a grid demo to include optional jitter. You could create a random list of points with something like

``````rows = 8
columns = 10
gap = [.1,.1]
jitter = .05
points = []
for Jdx in range (rows):
for Idx in range(columns):
points.append([(1+Idx-(columns+1)/2)*gap[0]+random()*jitter-random()*jitter,((rows+1)/2-Jdx-1)*gap[1]+random()*jitter-random()*jitter])
shuffle(points)
``````

Then use points[trials.thisN%len(points)] for the location of an object in a loop called trials. %len(points) means that it will go back to the start once all points have been used.

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