The D3 bar graph is displaying a height value of "Not a Number"

Question

The D3 bar graph is displaying a height value of "Not a Number"

I'm working on incorporating a simple animated bar-chart into my webpage using the D3 (v7) library. This is part of a Django project, so the data for the chart is coming from my views.py file. However, when I try to display the chart, only part of it shows up on the page. The x and y axis lines along with the labels are visible, but there's an error message that says:

Error: <rect> attribute height: Expected length, "NaN".

Below is the relevant section from my HTML template:

<div id="chart-container"></div>

        <script src="https://d3js.org/d3.v7.min.js"></script>

        <script type="text/javascript">
          const data = JSON.parse('{{ assign_levels|safe }}');

          // Rest of the JavaScript code for generating the chart here...
      
      </script>

Additionally, here is the data input for the chart:

[["Class", 36], ["School - cluster", 6], ["Individual", 20], ["N", 1], ["School - multi-site", 9], ["Not provided/ not available", 4], ["Region or district", 1]]

I'm perplexed by the error message regarding the "NaN" height value because I've clearly set the height to an absolute value like 500 pixels in the code.

javascript python-3.x django d3.js

Answer 1

Answer №1

You've provided an array of arrays as data, but the D3 code is designed to work with an array of objects with specific keys. I have modified the data format to be an array of objects.

To make this change in your code, follow the example below:

const rawData = JSON.parse('{{ assign_levels|safe }}');
const data = rawData.map(d => ({level_assign: d[0], count: d[1]}));

This adjustment will transform your data into a structured format rather than a list of arrays.

[
  {"level_assign": "Class", "count": 36},
  {"level_assign": "School - cluster", "count": 6},
  {"level_assign": "Individual", "count": 20},
  {"level_assign": "N", "count": 1},
  {"level_assign": "School - multi-site", "count": 9},
  {"level_assign": "Not provided/ not available", "count": 4},
  {"level_assign": "Region or district", "count": 1}
]

To see an example with full code implementation:

//script.js
const rawData = [
    ["Class", 36],
    ["School - cluster", 6],
    ["Individual", 20],
    ["N", 1],
    ["School - multi-site", 9],
    ["Not provided/ not available", 4],
    ["Region or district", 1],
];

const data = rawData.map((d) => ({
    level_assign: d[0],
    count: d[1]
}));

// Rest of the D3 visualization code...

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>D3 Bar Chart</title>
</head>
<body>
    <div id="chart-container"></div>

    <script src="https://d3js.org/d3.v7.min.js"></script>
    <script src="script.js"></script>
</body>
</html>

Answer 2

You've provided an array of arrays as data, but the D3 code is designed to work with an array of objects with specific keys. I have modified the data format to be an array of objects.

To make this change in your code, follow the example below:

const rawData = JSON.parse('{{ assign_levels|safe }}');
const data = rawData.map(d => ({level_assign: d[0], count: d[1]}));

This adjustment will transform your data into a structured format rather than a list of arrays.

[
  {"level_assign": "Class", "count": 36},
  {"level_assign": "School - cluster", "count": 6},
  {"level_assign": "Individual", "count": 20},
  {"level_assign": "N", "count": 1},
  {"level_assign": "School - multi-site", "count": 9},
  {"level_assign": "Not provided/ not available", "count": 4},
  {"level_assign": "Region or district", "count": 1}
]

To see an example with full code implementation:

//script.js
const rawData = [
    ["Class", 36],
    ["School - cluster", 6],
    ["Individual", 20],
    ["N", 1],
    ["School - multi-site", 9],
    ["Not provided/ not available", 4],
    ["Region or district", 1],
];

const data = rawData.map((d) => ({
    level_assign: d[0],
    count: d[1]
}));

// Rest of the D3 visualization code...

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>D3 Bar Chart</title>
</head>
<body>
    <div id="chart-container"></div>

    <script src="https://d3js.org/d3.v7.min.js"></script>
    <script src="script.js"></script>
</body>
</html>

Answer 3

Answer №2

When working with the Python pandas library, you may encounter situations where an empty result is represented as NaN (which stands for "Not a Number"). To address this issue, you can utilize the fillna method to replace these NaN values with a specified value within your dataframe:

df = df.fillna('')

By implementing this change, you should be able to resolve any display problems downstream. However, it is essential to investigate further to determine why these NaN values are being generated in the first place.

Answer 4

When working with the Python pandas library, you may encounter situations where an empty result is represented as NaN (which stands for "Not a Number"). To address this issue, you can utilize the fillna method to replace these NaN values with a specified value within your dataframe:

df = df.fillna('')

By implementing this change, you should be able to resolve any display problems downstream. However, it is essential to investigate further to determine why these NaN values are being generated in the first place.

The D3 bar graph is displaying a height value of "Not a Number"

Answer №1

Answer №2

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