Mix Razor and Javascript code
Use <text>:
<script type="text/javascript"> var data = []; @foreach (var r in Model.rows) { <text> data.push([ @r.UnixTime * 1000, @r.Value ]); </text> }</script>
Inside a code block (eg, @foreach), you need to mark the markup (or, in this case, Javascript) with @: or the <text> tag.
Inside the markup contexts, you need to surround code with code blocks (@{ ... } or @if, ...)
you also can simply use
<script type="text/javascript"> var data = []; @foreach (var r in Model.rows) { @:data.push([ @r.UnixTime * 1000, @r.Value ]); }</script>note @: