datashade_yaxis_flip.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "import numpy as np\n",
    "import xarray as xr\n",
    "import hvplot.xarray\n",
    "from holoviews import opts"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "arr = np.arange(2000000).reshape(2000, 1000)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da = xr.DataArray(\n",
    "    data=arr,\n",
    "    dims=['x','y'],\n",
    "    coords = {\n",
    "        'x':np.arange(2000),\n",
    "        'y':np.arange(1000,0, -1)\n",
    "    }\n",
    ")\n",
    "da"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "#### Create anomaly in a corner, note the descending y-axis, but using positional indexing:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da[100:200, 100:200] = 100"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Anomaly placed at coordinates (100:200, 800:900)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da.hvplot(x='x', y='y', colorbar=False, data_aspect=1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Using datashade = True, anomaly shows at (100:200, 100:200)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da.hvplot(datashade=True, x='x', y='y', data_aspect=1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "### Presume: Descending coordinates are the problem"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da2 = np.flip(da, 1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da2"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "> Note the now ascending y coordinate !!\n",
    "\n",
    "### Plotting without datashade shows the correct and same thing, despite the flip\n",
    "... because the default plotter uses always ascending coordinates"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da2.hvplot(x='x', y='y', colorbar=False, data_aspect=1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### and suddenly, using datashade is fine:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da2.hvplot(x='x', y='y', datashade=True, data_aspect=1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Does x-axis have same problem?"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da3 = xr.DataArray(\n",
    "    data=arr,\n",
    "    dims=['x','y'],\n",
    "    coords = {\n",
    "        'x':np.arange(2000, 0, -1),\n",
    "        'y':np.arange(1000)\n",
    "    }\n",
    ")\n",
    "da3"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da3[100:200, 100:200] = 100"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da3.hvplot(x='x', y='y', colorbar=False, data_aspect=1)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Yep, same problem here:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": [
    "da.hvplot(x='x', y='y', datashade=True, data_aspect=1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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