# 109. Setting the values of an array section
topic: {ref}`arrays`
```{note}
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```
Fortran array indices must be integers, so you cannot write
v(v<0) = -1
as in R, but alternatives are
where (v<0) v = -1
v = merge(-1,v,v<0)
v(truloc(v<0)) = -1
where truloc is a user function that creates a vector subscript from a logical mask.
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