What determines the column order of a table data view mapping?

In my capabilities.json, I have data roles defined like this:

"dataRoles": [
	{"displayName": "Measured Depth", "name": "measuredDepth", "kind": "Grouping"},
	{"displayName": "Is Planned", "name": "isPlanned", "kind": "Grouping"},
	{"displayName": "Is Actual", "name": "isActual", "kind": "Grouping"},
	{"displayName": "Depth Above", "name": "depthAbove", "kind": "Grouping"},
	{"displayName": "Planned TVD", "name": "plannedTrueVerticalDepth", "kind": "Grouping"},
	{"displayName": "Depth Below", "name": "depthBelow", "kind": "Grouping"},
	{"displayName": "Actual TVD", "name": "actualTrueVerticalDepth", "kind": "Grouping"},
	{"displayName": "Dog Leg Severity", "name": "dogLegSeverity", "kind": "Grouping"}
]

And my data view mapping looks like this:

"dataViewMappings": [{
	"table": {"rows": { "select": [
		{"for": {"in": "measuredDepth"}},
		{"for": {"in": "isPlanned"}},
		{"for": {"in": "isActual"}},
		{"for": {"in": "depthAbove"}},
		{"for": {"in": "plannedTrueVerticalDepth"}},
		{"for": {"in": "depthBelow"}},
		{"for": {"in": "actualTrueVerticalDepth"}},
		{"for": {"in": "dogLegSeverity"}}
	]}}
}]

And yet, when I look at my row data in the javascript debugger, the columns do not come in that order (abbreviated):

{
	"0": {"roles": {"isActual": true}},
	"1": {"roles": {"isPlanned": true}},
	"2": {"roles": {"depthAbove": true}},
	"3": {"roles": {"plannedTrueVerticalDepth": true}},
	"4": {"roles": {"depthBelow": true}},
	"5": {"roles": {"actualTrueVerticalDepth": true}},
	"6": {"roles": {"dogLegSeverity": true}},
	"7": {"roles": {"measuredDepth": true}}
}

Is this normal, or did I set something up wrong?  Do I need to scan the columns and dynamically locate my data points on each refresh?  I sort of thought the data view mapping would handle that.