Created on Skills Network Labs

percentage_summary.ipynb

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   "cell_type": "markdown",
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   "source": [
    "# Calculate a summary table with percentages per group"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "R automatically includes the dataset `mtcars`. From this we will select the cylinders (`cyl`) and gears (`gear`) as grouping categories and produce a summary table which includes counts and percentages. For this we will need to load the `tidyverse`."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [],
   "source": [
    "library(tidyverse)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "First you select which variables to `group_by`. Then `tally` created the summary total numbers `n`. Finally, `mutate` will create a new column for the percentages of the groups."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "<table>\n",
       "<caption>A grouped_df: 8 × 4</caption>\n",
       "<thead>\n",
       "\t<tr><th scope=col>cyl</th><th scope=col>gear</th><th scope=col>n</th><th scope=col>percent</th></tr>\n",
       "\t<tr><th scope=col>&lt;dbl&gt;</th><th scope=col>&lt;dbl&gt;</th><th scope=col>&lt;int&gt;</th><th scope=col>&lt;chr&gt;</th></tr>\n",
       "</thead>\n",
       "<tbody>\n",
       "\t<tr><td>4</td><td>3</td><td> 1</td><td>9.09 % </td></tr>\n",
       "\t<tr><td>4</td><td>4</td><td> 8</td><td>72.73 %</td></tr>\n",
       "\t<tr><td>4</td><td>5</td><td> 2</td><td>18.18 %</td></tr>\n",
       "\t<tr><td>6</td><td>3</td><td> 2</td><td>28.57 %</td></tr>\n",
       "\t<tr><td>6</td><td>4</td><td> 4</td><td>57.14 %</td></tr>\n",
       "\t<tr><td>6</td><td>5</td><td> 1</td><td>14.29 %</td></tr>\n",
       "\t<tr><td>8</td><td>3</td><td>12</td><td>85.71 %</td></tr>\n",
       "\t<tr><td>8</td><td>5</td><td> 2</td><td>14.29 %</td></tr>\n",
       "</tbody>\n",
       "</table>\n"
      ],
      "text/latex": [
       "A grouped\\_df: 8 × 4\n",
       "\\begin{tabular}{llll}\n",
       " cyl & gear & n & percent\\\\\n",
       " <dbl> & <dbl> & <int> & <chr>\\\\\n",
       "\\hline\n",
       "\t 4 & 3 &  1 & 9.09 \\% \\\\\n",
       "\t 4 & 4 &  8 & 72.73 \\%\\\\\n",
       "\t 4 & 5 &  2 & 18.18 \\%\\\\\n",
       "\t 6 & 3 &  2 & 28.57 \\%\\\\\n",
       "\t 6 & 4 &  4 & 57.14 \\%\\\\\n",
       "\t 6 & 5 &  1 & 14.29 \\%\\\\\n",
       "\t 8 & 3 & 12 & 85.71 \\%\\\\\n",
       "\t 8 & 5 &  2 & 14.29 \\%\\\\\n",
       "\\end{tabular}\n"
      ],
      "text/markdown": [
       "\n",
       "A grouped_df: 8 × 4\n",
       "\n",
       "| cyl &lt;dbl&gt; | gear &lt;dbl&gt; | n &lt;int&gt; | percent &lt;chr&gt; |\n",
       "|---|---|---|---|\n",
       "| 4 | 3 |  1 | 9.09 %  |\n",
       "| 4 | 4 |  8 | 72.73 % |\n",
       "| 4 | 5 |  2 | 18.18 % |\n",
       "| 6 | 3 |  2 | 28.57 % |\n",
       "| 6 | 4 |  4 | 57.14 % |\n",
       "| 6 | 5 |  1 | 14.29 % |\n",
       "| 8 | 3 | 12 | 85.71 % |\n",
       "| 8 | 5 |  2 | 14.29 % |\n",
       "\n"
      ],
      "text/plain": [
       "  cyl gear n  percent\n",
       "1 4   3     1 9.09 % \n",
       "2 4   4     8 72.73 %\n",
       "3 4   5     2 18.18 %\n",
       "4 6   3     2 28.57 %\n",
       "5 6   4     4 57.14 %\n",
       "6 6   5     1 14.29 %\n",
       "7 8   3    12 85.71 %\n",
       "8 8   5     2 14.29 %"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "mtcars %>%\n",
    "  group_by(cyl, gear) %>%\n",
    "  tally() %>%\n",
    "  mutate(percent = paste(round((n/sum(n)) * 100, digits = 2), \"%\"))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Everything in the percentage column should add up to `3` since there are three overall gear groups. `pull` returns the last column (i.e. the `percentage` in this case)."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/html": [
       "3"
      ],
      "text/latex": [
       "3"
      ],
      "text/markdown": [
       "3"
      ],
      "text/plain": [
       "[1] 3"
      ]
     },
     "metadata": {},
     "output_type": "display_data"
    }
   ],
   "source": [
    "mtcars %>% group_by(cyl, gear) %>% tally() %>% mutate(percentage = n/sum(n)) %>% pull() %>% sum()"
   ]
  }
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