Interactive Line Charts

When to reach for a line chart

A line chart is the go-to shape for change over an ordered axis — almost always time (days, months, years). The line itself draws attention to trend: is the metric rising, falling, or flat? Markers on top of the line let you also read off exact points without losing the trend shape.

Basic interactive line

import pandas as pd
import plotly.express as px
 
df = pd.DataFrame({
    "date": pd.date_range("2025-01-01", periods=7, freq="D"),
    "orders": [120, 140, 130, 160, 155, 170, 180],
})
 
fig = px.line(df, x="date", y="orders", markers=True, title="Daily orders")
fig.show()

Because this is Plotly (not Matplotlib), the rendered chart already lets you hover each marker for its exact date/value, drag to zoom into a date range, and double-click to reset.

Multiple lines (color)

import pandas as pd
import plotly.express as px
 
df = pd.DataFrame({
    "date": list(pd.date_range("2025-01-01", periods=5, freq="D")) * 2,
    "orders": [120, 140, 130, 160, 155, 100, 110, 120, 125, 140],
    "product": ["A"] * 5 + ["B"] * 5,
})
 
fig = px.line(df, x="date", y="orders", color="product", markers=True, title="Orders by product")
fig.show()

Passing color="product" does two things at once: it splits the data into one line per group, and it adds a legend you can click to hide/show a series.

Tips

• Use hover_data=[...] to show extra fields (e.g. region, channel) in the tooltip.
• Use fig.update_layout(...) for axis labels, margins, and legend position.
• Sort your DataFrame by the x-axis column first — Plotly draws points in row order, so an unsorted date column produces a zig-zag line.

  flowchart TD
  A["Is the x-axis ordered
and continuous (time, sequence)?"] -->|"Yes"| B["Does trend/direction
matter most?"]
  A -->|"No, unordered categories"| C["Use a bar chart instead"]
  B -->|"Yes"| D["px.line(...)
add markers=True for exact points"]
  B -->|"No, comparing totals"| C

Check your understanding

Next

Continue to: Interactive Bar Charts for comparing categories.

🧪 Try It Yourself

Exercise 1 – Draw a Line Chart

Press Run to see what your code prints.

Exercise 2 – Show the Markers

Press Run to see what your code prints.

Exercise 3 – One Line per Group

Press Run to see what your code prints.