Data visualization with Kandy

Kotlin offers an all-in-one-place solution for powerful and flexible data visualization, providing an intuitive way to present and explore data before diving into complex models.

This tutorial demonstrates how to create different chart types in IntelliJ IDEA using Kotlin Notebook with the Kandy and Kotlin DataFrame libraries.

Before you start

Kotlin Notebook relies on the Kotlin Notebook plugin, which is bundled and enabled in IntelliJ IDEA by default.

If the Kotlin Notebook features are not available, ensure the plugin is enabled. For more information, see Set up an environment.

To follow this tutorial:

Create a new Kotlin Notebook.
In your notebook, import Kandy and Kotlin DataFrame:
%use kandy %use dataframe

Create a DataFrame

To start, let's create a DataFrame with data to visualize. This DataFrame stores simulated monthly average temperatures for Berlin, Madrid, and Caracas:

// The months variable stores a list with the 12 months of the year
val months = listOf(
    "January", "February",
    "March", "April", "May",
    "June", "July", "August",
    "September", "October", "November",
    "December"
)
// The tempBerlin, tempMadrid, and tempCaracas variables store a list 
// with temperature values for each month
val tempBerlin =
    listOf(-0.5, 0.0, 4.8, 9.0, 14.3, 17.5, 19.2, 18.9, 14.5, 9.7, 4.7, 1.0)
val tempMadrid =
    listOf(6.3, 7.9, 11.2, 12.9, 16.7, 21.1, 24.7, 24.2, 20.3, 15.4, 9.9, 6.6)
val tempCaracas =
    listOf(27.5, 28.9, 29.6, 30.9, 31.7, 35.1, 33.8, 32.2, 31.3, 29.4, 28.9, 27.6)

Now let's create a new variable (df) and use the dataFrameOf() function to generate a DataFrame of three columns (Month, Temperature, and City):

val df = dataFrameOf(
    "Month" to months + months + months,
    "Temperature" to tempBerlin + tempMadrid + tempCaracas,
    "City" to List(12) { "Berlin" } + List(12) { "Madrid" } + List(12) { "Caracas" }
)

To preview the data, use the .head() function:

df.head(4) // Returns the first four rows

In our dataset, the first four rows store temperature in Berlin from January to April:

Create a line chart

Let's create a line chart in Kotlin Notebook using the df DataFrame from the previous section:

Call the .plot() function from the Kandy library.
Apply the line() layer.
Map the Month and Temperature columns to the X and Y axes accordingly.
(Optional) Customize colors and sizes.

df.plot {
   line {
      x(Month)
      y(Temperature)

      color(City) {
         scale = categorical(
            "Berlin" to Color.hex("#6F4E37"),
            "Madrid" to Color.hex("#C2D4AB"),
            "Caracas" to Color.hex("#B5651D")
         )
      }
      width = 1.5
   }
   layout {
      size = 1000 to 450
   }
}

Here's the result:

Create a points chart

Now, let's visualize the df DataFrame in a points (scatter) chart:

Call the .plot() function from the Kandy library.
Apply the points() layer.
Map the Month and Temperature columns to the X and Y axes accordingly.
(Optional) Customize colors, axis labels, point sizes, and chart title.

df.plot {
   points {
      x(Month) {
         axis.name = "Month"
      }
      y(Temperature) {
         axis.name = "Temperature"
      }

      color(City) {
         scale = categorical(
            "Berlin" to Color.hex("#6F4E37"),
            "Madrid" to Color.hex("#C2D4AB"),
            "Caracas" to Color.hex("#B5651D")
         )
      }
      size = 5.5
   }
   layout {
      title = "Temperature per month"
   }
}

Here's the result:

Create a bar chart

Finally, let's create a bar chart for each city:

Use the .groupBy() function to group the DataFrame by the City column.
Call the plot() function from the Kandy library.
Apply the bars() layer.
(Optional) Add a title for the chart, customize colors.

df.groupBy { City }.plot {
    bars {
        x(Month)
        y(Temperature)
        
        fillColor(City) {
            scale = categorical(
                "Berlin" to Color.hex("#6F4E37"),
                "Madrid" to Color.hex("#C2D4AB"),
                "Caracas" to Color.hex("#B5651D")
            )
        }
    }
    layout.title {
       title = "Temperature per month"
    }
}

Here's the result:

What's next

Explore more chart examples in the Kandy library documentation
Explore more advanced plotting options in the Lets-Plot library documentation
Find additional information about creating, exploring, and managing data frames in the Kotlin DataFrame library documentation
Learn more about data visualization in Kotlin Notebook in this YouTube video

13 May 2026