Need help comparing current index item to previous index item in a foreach loop

Hello All,

I'm currently creating an editable grid for school records with a field called year graduated. I want the following entries for this field to be compared with previous row to check if the year is greater than the previous row and output an error message. However, I can't seem to find a way to access the previous item. I tried using index function but I'm having a cannot index type error.

a!integerField(
    label: "Graduation Year/Expected Year",
    labelPosition: "ABOVE",
    value: fv!item.yearGraduated,
    saveInto: fv!item.yearGraduated,
    required: true,
    validations: {
        if(
            fv!index >= 2,
            if(
                fv!item.yearGraduated > index(fv!item.yearGraduated, fv!index - 1),
                "Please enter a valid year",
                ""
                ),
                ""
            )
    }
)

Any help would be appreciated.