---
url: /technical/process-mapping-date-to-date-date-to-prior-year-date.md
---

# Mapping.Date to Date.Date to Prior Year Date

The below code builds a mapping from Date elements to prior year **Date** elements. For each **Date** element in the **Date List** hierarchy, it maps back one year to that prior year date.

End outcome would be `Date:2016-01-01` maps to `date:2015-01-01`.

## Process Code

```vb
var mapName = "Mapping.Date to Date.Date to Prior Year Date";
var lDims = ["Date"];
var rDims = ["Date"];

function pre() {
    // This function is called once before the processes is executed.
    // Use this to setup prompts.
    script.log('process pre-execution parameters parsed.');
}

function begin() {
    // This function is called once at the start of the process
    script.log('process execution started.');

    if (mapping.exists(mapName)) {
        mapping.wipe(mapName);
    } else {
        mapping.create(mapName, lDims, rDims, false, true);
    }

    let dates = JSON.parse(hierarchy.rootElements("Date", "Date List"));

    for (let i = 0; i < dates.length; i++) {
        let date = dates[i];
        let year = date.substring(0, 4);

        let lastYear = (Number(year) - 1).toString()

        let lastYearDate = date.replace(year, lastYear)
        if (hierarchy.hasMember("Date", "Default", lastYearDate)) {
            mapping.rowAdd(mapName, [date], [lastYearDate]);
        }

        if (script.IsCancelled()) {
            return;
        }
    }

}

function data(record) {
    // This function is called once for each line of data on the second cycle
    // Use this to build dimensions and push data into cubes
}

function end() {
    // This function is called once at the end of the process
    script.log('process execution finished.');
}
```