Tableau for Data Analysts

What is Tableau?

Tableau is one of the world's leading data visualisation platforms. It is known for its drag-and-drop interface, its ability to connect to a vast range of data sources, and the quality and interactivity of its visualisations. Tableau is widely used in data-focused organisations, particularly in the US and UK technology and finance sectors.

Tableau comes in several versions:

• Tableau Desktop: The full authoring tool. Paid license.
• Tableau Public: Free version with limited connectivity and public publishing only. Excellent for learning and portfolio building.
• Tableau Server / Tableau Cloud: Enterprise publishing and sharing platforms.

For learning, use Tableau Public (public.tableau.com). You can publish your work publicly, which is also good for portfolios.

Tableau vs Power BI

Both tools are valuable skills. Power BI is stronger for complex data modelling and Microsoft environments. Tableau is stronger for creative, exploratory, pixel-perfect visualisation.

The Tableau Interface

Data Source page: Connect to data, join tables, create calculated fields.

Worksheet: Build individual charts. Contains:

• Dimensions shelf (left): Categorical fields (blue pills)
• Measures shelf (left): Numeric fields (green pills)
• Rows shelf: Drag fields here to determine the y-axis
• Columns shelf: Drag fields here to determine the x-axis
• Marks card: Control colour, size, shape, label, and detail
• Filter shelf: Add filters to the view

Dashboard: Assemble multiple worksheets into a single interactive view.

Story: A sequence of dashboard/worksheet points for presentations.

Dimensions and Measures

In Tableau, fields are automatically classified as:

• Dimensions (blue): Categorical or text fields that define the level of detail (Product Name, Country, Order Date when used for grouping)
• Measures (green): Numeric fields that are aggregated (Revenue, Quantity, Profit)

You can change the classification by right-clicking a field. Tableau automatically applies an aggregation (SUM by default) to measures.

Building Basic Charts

Bar Chart

1. Drag a Dimension to Rows (e.g., Category)
2. Drag a Measure to Columns (e.g., SUM(Sales))
3. Tableau automatically creates a bar chart

Click "Sort Descending" in the toolbar to sort bars by value.

Line Chart

1. Drag a Date field to Columns
2. Drag a Measure to Rows
3. Tableau creates a line chart (ensure the date is set to continuous)

Scatter Plot

1. Drag a measure to Columns (x-axis)
2. Drag another measure to Rows (y-axis)
3. Drag a Dimension to the Marks card > Detail (to plot one dot per record)

Show Me

The "Show Me" panel (top right) shows recommended chart types for the current field selection. Click a chart type to apply it automatically.

Calculated Fields

Create new fields using Tableau's calculation language:

// Profit Margin
[Profit] / [Sales]

// Customer Segment
IF [Sales] >= 10000 THEN "VIP"
ELSEIF [Sales] >= 5000 THEN "Gold"
ELSE "Standard"
END

// Year-over-Year Growth
(SUM([Sales]) - LOOKUP(SUM([Sales]), -1)) / ABS(LOOKUP(SUM([Sales]), -1))

// Days Since Order
DATEDIFF('day', [Order Date], TODAY())

Filters in Tableau

Dimension Filters

1. Drag a dimension to the Filters shelf
2. Select which values to include/exclude

Measure Filters

1. Drag a measure to the Filters shelf
2. Set a range, minimum, or maximum

Quick Filters (Slicers)

Right-click a field in the Filters shelf > Show Filter

This creates a filter control that viewers can interact with. You can connect a filter to multiple worksheets on a dashboard (right-click > Apply to Worksheets > All Using This Data Source).

Building a Dashboard

1. Click the "New Dashboard" tab at the bottom
2. Drag worksheets from the left panel onto the canvas
3. Arrange and resize them
4. Add actions (Dashboard > Actions) for interactive filtering between sheets
5. Add filter controls, text, and images from the Objects panel on the left

Dashboard Actions

Actions enable interactivity:

• Filter Action: Clicking a data point in one chart filters other charts on the dashboard
• Highlight Action: Clicking highlights related data across charts
• URL Action: Clicking opens a URL

Tableau LOD Expressions

Level of Detail (LOD) expressions are one of Tableau's most powerful features. They allow calculations at different levels of granularity than the view's current level of detail.

// FIXED: Calculate at a specified level regardless of the view
{ FIXED [Customer ID] : SUM([Sales]) }
// Returns each customer's total sales, regardless of what's in the view

// INCLUDE: Calculate at a more granular level than the view
{ INCLUDE [Order ID] : SUM([Sales]) }

// EXCLUDE: Calculate at a coarser level than the view
{ EXCLUDE [Month] : SUM([Sales]) }
// Returns total annual sales even when the view is at monthly level

LOD expressions are the Tableau equivalent of window functions in SQL.

Key Takeaways

• Tableau is a leading visualisation platform known for drag-and-drop ease and high-quality interactivity -- Tableau Public is free for learning and portfolio work.
• Tableau classifies fields as Dimensions (blue, categorical) or Measures (green, numeric) and automatically applies aggregations to measures.
• Build charts by dragging dimensions and measures to Rows, Columns, and the Marks card -- Show Me recommends appropriate chart types for your selection.
• Dashboard Actions enable cross-filtering and highlighting between worksheets -- click a data point in one chart to filter all others on the dashboard.
• LOD (Level of Detail) expressions calculate metrics at a different granularity than the current view -- the Tableau equivalent of SQL window functions.

Practice Exercise

In Tableau Public:

1. Connect to the Sample - Superstore dataset (included by default)
2. Create a worksheet: revenue by category, sorted descending (bar chart)
3. Create a worksheet: monthly sales trend for 2023 (line chart)
4. Create a worksheet: profit vs sales scatter plot coloured by region
5. Build a dashboard combining all three worksheets with a Year filter that applies to all sheets
6. Add a filter action so clicking a category in chart 1 filters the line chart and scatter plot
7. Publish to Tableau Public and share the link