xarray 0.10.0 time decoding round-off error

xr-decode-times-roundoff.ipynb

{
 "cells": [
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [],
   "source": [
    "import xarray as xr"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [],
   "source": [
    "from xarray.conventions import decode_cf_datetime"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'0.10.0'"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "xr.__version__"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [],
   "source": [
    "#!curl -O ftp://ftp.chg.ucsb.edu/pub/org/chg/products/CHIRPS-2.0/global_daily/netcdf/p05/by_month/chirps-v2.0.1983.01.days_p05.nc"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [],
   "source": [
    "infile = 'chirps-v2.0.1983.01.days_p05.nc'"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<xarray.DataArray 'time' (time: 31)>\n",
       "array(['1982-12-31T23:59:59.560122368', '1983-01-02T00:00:05.712183296',\n",
       "       '1983-01-03T00:00:03.274309632', '1983-01-04T00:00:00.836435968',\n",
       "       '1983-01-05T00:00:06.988496896', '1983-01-06T00:00:04.550623232',\n",
       "       '1983-01-07T00:00:02.112749568', '1983-01-07T23:59:59.674875904',\n",
       "       '1983-01-09T00:00:05.826936832', '1983-01-10T00:00:03.389063168',\n",
       "       '1983-01-11T00:00:00.951189504', '1983-01-12T00:00:07.103250432',\n",
       "       '1983-01-13T00:00:04.665376768', '1983-01-14T00:00:02.227503104',\n",
       "       '1983-01-14T23:59:59.789629440', '1983-01-16T00:00:05.941690368',\n",
       "       '1983-01-17T00:00:03.503816704', '1983-01-18T00:00:01.065943040',\n",
       "       '1983-01-19T00:00:07.218003968', '1983-01-20T00:00:04.780130304',\n",
       "       '1983-01-21T00:00:02.342256640', '1983-01-21T23:59:59.904382976',\n",
       "       '1983-01-23T00:00:06.056443904', '1983-01-24T00:00:03.618570240',\n",
       "       '1983-01-25T00:00:01.180696576', '1983-01-26T00:00:07.332757504',\n",
       "       '1983-01-27T00:00:04.894883840', '1983-01-28T00:00:02.457010176',\n",
       "       '1983-01-29T00:00:00.019136512', '1983-01-30T00:00:06.171197440',\n",
       "       '1983-01-31T00:00:03.733323776'], dtype='datetime64[ns]')\n",
       "Coordinates:\n",
       "  * time     (time) datetime64[ns] 1982-12-31T23:59:59.560122368 ...\n",
       "Attributes:\n",
       "    standard_name:  time\n",
       "    axis:           T"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ds = xr.open_dataset(infile, decode_times=True)\n",
    "ds.time"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array(['1982-12-31T23:59:59.560122368', '1983-01-02T00:00:05.712183296',\n",
       "       '1983-01-03T00:00:03.274309632', '1983-01-04T00:00:00.836435968',\n",
       "       '1983-01-05T00:00:06.988496896', '1983-01-06T00:00:04.550623232',\n",
       "       '1983-01-07T00:00:02.112749568', '1983-01-07T23:59:59.674875904',\n",
       "       '1983-01-09T00:00:05.826936832', '1983-01-10T00:00:03.389063168',\n",
       "       '1983-01-11T00:00:00.951189504', '1983-01-12T00:00:07.103250432',\n",
       "       '1983-01-13T00:00:04.665376768', '1983-01-14T00:00:02.227503104',\n",
       "       '1983-01-14T23:59:59.789629440', '1983-01-16T00:00:05.941690368',\n",
       "       '1983-01-17T00:00:03.503816704', '1983-01-18T00:00:01.065943040',\n",
       "       '1983-01-19T00:00:07.218003968', '1983-01-20T00:00:04.780130304',\n",
       "       '1983-01-21T00:00:02.342256640', '1983-01-21T23:59:59.904382976',\n",
       "       '1983-01-23T00:00:06.056443904', '1983-01-24T00:00:03.618570240',\n",
       "       '1983-01-25T00:00:01.180696576', '1983-01-26T00:00:07.332757504',\n",
       "       '1983-01-27T00:00:04.894883840', '1983-01-28T00:00:02.457010176',\n",
       "       '1983-01-29T00:00:00.019136512', '1983-01-30T00:00:06.171197440',\n",
       "       '1983-01-31T00:00:03.733323776'], dtype='datetime64[ns]')"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "ds = xr.open_dataset(infile, decode_times=False)\n",
    "decode_cf_datetime(ds.time.values, units=ds.time.units, calendar=ds.time.calendar)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "<class 'netCDF4._netCDF4.Variable'>\n",
       "float32 time(time)\n",
       "    units: days since 1980-1-1 0:0:0\n",
       "    standard_name: time\n",
       "    calendar: gregorian\n",
       "    axis: T\n",
       "unlimited dimensions: \n",
       "current shape = (31,)\n",
       "filling on, default _FillValue of 9.969209968386869e+36 used"
      ]
     },
     "execution_count": 8,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "import netCDF4 as nc4\n",
    "dd = nc4.Dataset(infile)\n",
    "tvar = dd.variables['time']\n",
    "tvar"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "array([datetime.datetime(1983, 1, 1, 0, 0),\n",
       "       datetime.datetime(1983, 1, 2, 0, 0),\n",
       "       datetime.datetime(1983, 1, 3, 0, 0),\n",
       "       datetime.datetime(1983, 1, 4, 0, 0),\n",
       "       datetime.datetime(1983, 1, 5, 0, 0),\n",
       "       datetime.datetime(1983, 1, 6, 0, 0),\n",
       "       datetime.datetime(1983, 1, 7, 0, 0),\n",
       "       datetime.datetime(1983, 1, 8, 0, 0),\n",
       "       datetime.datetime(1983, 1, 9, 0, 0),\n",
       "       datetime.datetime(1983, 1, 10, 0, 0),\n",
       "       datetime.datetime(1983, 1, 11, 0, 0),\n",
       "       datetime.datetime(1983, 1, 12, 0, 0),\n",
       "       datetime.datetime(1983, 1, 13, 0, 0),\n",
       "       datetime.datetime(1983, 1, 14, 0, 0),\n",
       "       datetime.datetime(1983, 1, 15, 0, 0),\n",
       "       datetime.datetime(1983, 1, 16, 0, 0),\n",
       "       datetime.datetime(1983, 1, 17, 0, 0),\n",
       "       datetime.datetime(1983, 1, 18, 0, 0),\n",
       "       datetime.datetime(1983, 1, 19, 0, 0),\n",
       "       datetime.datetime(1983, 1, 20, 0, 0),\n",
       "       datetime.datetime(1983, 1, 21, 0, 0),\n",
       "       datetime.datetime(1983, 1, 22, 0, 0),\n",
       "       datetime.datetime(1983, 1, 23, 0, 0),\n",
       "       datetime.datetime(1983, 1, 24, 0, 0),\n",
       "       datetime.datetime(1983, 1, 25, 0, 0),\n",
       "       datetime.datetime(1983, 1, 26, 0, 0),\n",
       "       datetime.datetime(1983, 1, 27, 0, 0),\n",
       "       datetime.datetime(1983, 1, 28, 0, 0),\n",
       "       datetime.datetime(1983, 1, 29, 0, 0),\n",
       "       datetime.datetime(1983, 1, 30, 0, 0),\n",
       "       datetime.datetime(1983, 1, 31, 0, 0)], dtype=object)"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "nc4.num2date(tvar[:], units=tvar.units, calendar=tvar.calendar)"
   ]
  }
 ],
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