地図ライブラリにラインデータを渡す際にsource, targetをペアにしたデータに変換して渡したいときがあるので、その変換方法のメモ。

もととなるGeoJSON(ライン)

const geojson = {
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {},
      "geometry": {
        "type": "LineString",
        "coordinates": [
          [
            -1.0272216796875,
            47.97889140226657
          ],
          [
            -1.9720458984374998,
            47.743017409121826
          ],
          [
            -2.537841796875,
            48.05605376398125
          ],
          [
            -3.1256103515625,
            48.03034580796616
          ],
          [
            -4.04296875,
            48.25759852914997
          ],
          [
            -4.290161132812499,
            48.36354888898689
          ]
        ]
      }
    }
  ]
}

変換処理

const result =  geojson.features
  .map(d => d.geometry.coordinates)
  .flat()
  .reduce((a,c, i, array)=>{
  if(!array[i-1]) return a;
    a.push({ source: array[i - 1], target:c})
  return a;
},[])

console.log(result)
> [
	{
		"source": [
			-1.0272216796875,
			47.97889140226657
		],
		"target": [
			-1.9720458984374998,
			47.743017409121826
		]
	},
	{
		"source": [
			-1.9720458984374998,
			47.743017409121826
		],
		"target": [
			-2.537841796875,
			48.05605376398125
		]
	},
	{
		"source": [
			-2.537841796875,
			48.05605376398125
		],
		"target": [
			-3.1256103515625,
			48.03034580796616
		]
	},
	{
		"source": [
			-3.1256103515625,
			48.03034580796616
		],
		"target": [
			-4.04296875,
			48.25759852914997
		]
	},
	{
		"source": [
			-4.04296875,
			48.25759852914997
		],
		"target": [
			-4.290161132812499,
			48.36354888898689
		]
	}
]