How do I randomly generate numbers with a certain amount of probability?

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Robert Newman
Robert Newman 2019-5-12
回答： John D'Errico 2019-5-12
Hi there,
Brand new to programming so sorry if this is a dumb question.
I have two folders with twenty-four images each, one folder contains emotional images and the other folder contains non-emotional images. The images are to be displayed on the left and right side of the screen under four conditions:
Non-emotional on the left - Emotional on the right for 6 trials
Emotional on the left - Non-emotional on the right for 6 trials
Non-emotional on the left - Non-emotional on the right for 6 trials
Emotional on the left - Emotional on the right for 6 trials
I figure I can do something like this using if statements, for loops, and randomly generating 4 different integers. The problem is if I do this by generating a random integer from 1-4, I want to make sure no integer is generated more than 6 times, because that would mean that the condition occurs for more than 6 trials. How can I do this?
Alternatively, is there a better way to do what I want to do?
Thanks in advance,

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回答（1 个）

John D'Errico
John D'Errico 2019-5-12
As is often the case, I would suggest you are overthinking this.
You have a sequence of 24 pairs of images to be shown. There will be 6 trials each for each combination. (At each trial, I assume you will randomly choose a pair of images from each folder. But that is not relevant at this point.)
So, consider what this matrix would indicate, assuming that a 1 indicates a non-emotional picture, and 2 indicates a choice from the set of emotional images.
trials = repmat([1 2;2 1;1 1;2 2],6,1);
trials = trials(randperm(24),:)
trials =
2 2
2 1
2 1
1 2
2 2
2 1
1 2
...
Each combination occurs exactly 6 times, in randomly permuted order.

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