update README

Author: mbostock

README.md

@@ -1258,6 +1258,8 @@ The following window reducers are supported:
 * *difference* - the difference between the last and first window value
 * *ratio* - the ratio of the last and first window value
 
+By default, **shift** is *centered* and **reduce** is *mean*.
+
 #### Plot.map(*outputs*, *options*)
 
 ```js
@@ -1282,37 +1284,37 @@ Plot.mapY("cumsum", {y: d3.randomNormal()})
 
 Equivalent to Plot.map({y: *map*, y1: *map*, y2: *map*}, *options*), but ignores any of **y**, **y1**, and **y2** not present in *options*.
 
-#### Plot.normalizeX(*options*)
+#### Plot.normalizeX(*basis*, *options*)
 
 ```js
 Plot.normalizeX({y: "Date", x: "Close", stroke: "Symbol"})
 ```
 
-Like [Plot.mapX](#plotmapxmap-options), but applies the normalize map method with the given *options*.
+Like [Plot.mapX](#plotmapxmap-options), but applies the normalize map method with the given *basis*.
 
-#### Plot.normalizeY(*options*)
+#### Plot.normalizeY(*basis*, *options*)
 
 ```js
 Plot.normalizeY({x: "Date", y: "Close", stroke: "Symbol"})
 ```
 
-Like [Plot.mapY](#plotmapymap-options), but applies the normalize map method with the given *options*.
+Like [Plot.mapY](#plotmapymap-options), but applies the normalize map method with the given *basis*.
 
-#### Plot.windowX(*options*)
+#### Plot.windowX(*k*, *options*)
 
 ```js
-Plot.windowX({y: "Date", x: "Anomaly", k: 24})
+Plot.windowX(24, {y: "Date", x: "Anomaly"})
 ```
 
-Like [Plot.mapX](#plotmapxmap-options), but applies the window map method with the given *options*.
+Like [Plot.mapX](#plotmapxmap-options), but applies the window map method with the given window size *k*. If *k* is an object, separate *shift* and *reduce* window options can also be specified.
 
-#### Plot.windowY(*options*)
+#### Plot.windowY(*k*, *options*)
 
 ```js
-Plot.windowY({x: "Date", y: "Anomaly", k: 24})
+Plot.windowY(24, {x: "Date", y: "Anomaly"})
 ```
 
-Like [Plot.mapY](#plotmapymap-options), but applies the window map method with the given *options*.
+Like [Plot.mapY](#plotmapymap-options), but applies the window map method with the given window size *k*. If *k* is an object, separate *shift* and *reduce* window options can also be specified.
 
 ### Select
 

src/transforms/normalize.js

@@ -4,12 +4,12 @@ import {take} from "../mark.js";
 import {mapX, mapY} from "./map.js";
 
 export function normalizeX(basis, options) {
-  if (arguments.length === 1 && basis !== undefined) ({basis, ...options} = basis);
+  if (arguments.length === 1) ({basis, ...options} = basis);
   return mapX(normalize(basis), options);
 }
 
 export function normalizeY(basis, options) {
-  if (arguments.length === 1 && basis !== undefined) ({basis, ...options} = basis);
+  if (arguments.length === 1) ({basis, ...options} = basis);
   return mapY(normalize(basis), options);
 }