Adding comments to the code to answer issue3 - https://github.com/vaclavdekanovsky/data-analysis-in-examples/issues/3

Vizualizations/Plotly/Preprocess/Preprocessing.ipynb

@@ -26,7 +26,9 @@
     "We will use two datasets provided by the World Bank:\n",
     "    \n",
     "* International Arrival-- How many tourist have come to the country\n",
+    " * https://data.worldbank.org/indicator/ST.INT.ARVL\n",
     "* Receipts--How mach they spent in the country (how much the locals received)\n",
+    " * https://data.worldbank.org/indicator/ST.INT.RCPT.CD\n",
     "\n",
     "Because both dataset mix data for countries with regional aggregates, eg. `CEB` for Central Europe and Baltics.\n",
     "It also contains columns between `1960` and `2018` but data are populated since `1995` only. \n",
@@ -42,10 +44,10 @@
     "def process_world_bank_dataset(path):\n",
     "    df = pd.read_csv(path, skiprows=4)\n",
     "    \n",
-    "    # load country_codes\n",
+    "    # load country_codes (from https://en.wikipedia.org/wiki/List_of_ISO_3166_country_codes)\n",
     "    country_codes = pd.read_csv(\"Country_Codes.csv\")\n",
     "    \n",
-    "    # info about regions\n",
+    "    # info about regions (part of the world bank data package)\n",
     "    regions = pd.read_csv(\"Metadata.csv\")\n",
     "\n",
     "    # merge country codes to have only countries\n",
@@ -292,7 +294,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.8.3"
+   "version": "3.7.4"
   },
   "toc": {
    "base_numbering": 1,