import pl from "npm:nodejs-polars";

export function residuals(x: pl.Expr, y: pl.Expr): pl.Expr {
  const xM = x.minus(x.mean());
  const yM = y.minus(y.mean());
  const xMSQ = xM.pow(2);
  const beta = xM.dot(yM).div(xMSQ.sum());
  return yM.minus(beta.mul(xM));
}

export const fillzero = (
  value = 0.0001,
) => (pl.all().replaceStrict(0, value, pl.all()));

export const minmaxScale = (col: pl.Expr) =>
  (col.minus(col.min())).div(col.max().minus(col.min()));

export const standardScale = (col: pl.Expr) =>
  (col.minus(col.mean())).div(col.std());