Getting index of values that satisfy a condition for a list in R

First I create random p-values:

p_values <- runif(10, 0, 1)

 [1] 0.42179212 0.78151769 0.11912855 0.24357883 0.78714226 0.92601108 0.01192523 0.97904421 0.51560005 0.69564248

What you can do is order the p-values based on your certain criteria and select indices which is from the column ix, as @Vincent Guillemot also suggested in the comment. You can use the following code:

ord = sort(p_values, index = TRUE)
    
$x
 [1] 0.01192523 0.11912855 0.24357883 0.42179212 0.51560005 0.69564248 0.78151769 0.78714226 0.92601108 0.97904421

$ix
 [1]  7  3  4  1  9 10  2  5  6  8

ord$ix[ord$x <= 0.05]

Output:

[1] 7

Which means that the index 7 has a p-value lower than 0.05.