Though it is riddled with TypeScript ! operator, it does work...
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September 18, 2024 00:02
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elastic tabstop
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| // taken from https://observablehq.com/@shaunlebron/elastic-tabstops | |
| // rust impl. at https://github.com/BurntSushi/tabwriter | |
| // original impl. at https://nick-gravgaard.com/elastic-tabstops/ | |
| function range(stop: number): number[] | |
| function range(start: number, stop: number, step?: number): number[] | |
| function range(start: number, stop?: number, step = 1): number[] { | |
| if (stop === undefined) [start, stop] = [0, start] | |
| const result = [] | |
| for (let i = start; i < stop; i += step) { | |
| result.push(i) | |
| } | |
| return result | |
| } | |
| function splitArray<T>(array: T[], shouldSplit: (curr: T, prev: T) => boolean) { | |
| const n = array.length | |
| if (n === 0) return [] | |
| // get each position in the array where a split should occur | |
| let indexes = range(1, n).filter(i => shouldSplit(array[i]!, array[i - 1]!)) | |
| // insert start/end points | |
| indexes = [0, ...indexes, n] | |
| // group elements between the indexes | |
| return range(0, indexes.length - 1).map(i => array.slice(indexes[i], indexes[i + 1])) | |
| } | |
| function computeElasticTabs(text: string) { | |
| // We ignore the last cell of each line | |
| // since the standard says we only count cells _behind_ a tab character. | |
| const table = text.split('\n').map(line => line.split('\t').slice(0, -1)) | |
| // result objects | |
| const tableUnpruned = text.split('\n').map(line => line.split('\t')) | |
| const cellBlocks: Record<string, number> = {} // map a cell coordinate `${row},${col}` to a block index | |
| const blockWidths = [] // map a block index to a width | |
| // cells by coordinate | |
| const numRows = table.length | |
| const numCols = Math.max(...table.map(cells => cells.length)) | |
| const getCell = (r: number, c: number) => ({ r, c, text: table[r]![c] }) | |
| // for each column, we group cells into blocks | |
| for (const c of range(numCols)) { | |
| // Get every cell in this column. | |
| const column = range(numRows) | |
| .map(r => getCell(r, c)) | |
| .filter(({ text }) => text != null) | |
| // Group contiguous cells into blocks. | |
| const blocks = splitArray(column, (curr, prev) => curr.r !== prev.r + 1) | |
| // process each block | |
| for (const cells of blocks) { | |
| // compute block width | |
| const w = Math.max(...cells.map(({ text }) => text!.length)) | |
| // create a new index to identify this block | |
| const blockI = blockWidths.length | |
| // associate each of our cell coordinates to this block | |
| for (const { r } of cells) { | |
| cellBlocks[`${r},${c}`] = blockI | |
| } | |
| // store the width of the block | |
| blockWidths.push(w) | |
| } | |
| } | |
| return { table: tableUnpruned, cellBlocks, blockWidths } | |
| } | |
| // View the given text with the elastic tabs expanded into spaces. | |
| export function expandElasticTabs(text: string, { blockPad = 1, minBlockWidth = 3 } = {}) { | |
| const { table, cellBlocks, blockWidths } = computeElasticTabs(text) | |
| const expandCell = (r: number, c: number) => { | |
| const text = table[r]![c] | |
| const i = cellBlocks[`${r},${c}`] | |
| const w = Math.max(minBlockWidth, blockWidths[i!]!) | |
| return text!.padEnd(w) | |
| } | |
| const numRows = table.length | |
| const numCols = (r: number) => table[r]!.length | |
| const lines = range(numRows).map(r => { | |
| const cells = range(numCols(r)).map(c => expandCell(r, c)) | |
| const pad = ' '.repeat(blockPad) | |
| return cells.join(pad) | |
| }) | |
| return lines.join('\n') | |
| } |
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