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LAPIS

Plot the global distribution of all sequences in R

This tutorial will guide you through the process of plotting the global distribution of all sequences in R by fetching data from the open SARS-CoV-2 LAPIS API of CoV-Spectrum. It is able to aggregate data. You will learn how to query the API, check for errors and deprecation, parse data as a data frame, and create a plot using the ggplot2 package.

Prerequisites

You should have a basic understanding of R programming and the ggplot2 package.

Step 1: Query data from the LAPIS API

First, you will use the fromJSON function from the jsonlite package to query the LAPIS API:

library(jsonlite)
response <- fromJSON("https://lapis.cov-spectrum.org/open/sample/aggregated?fields=region")

The URL used in the query is structured as follows:

  • https://lapis.cov-spectrum.org/open: This is the base URL for the LAPIS instance.
  • /sample/aggregated: This endpoint retrieves aggregated data
  • ?fields=region: This query parameter specifies that we want to aggregate the data by the region field.

By querying this URL, you fetch the aggregated data on sequences stratified by their regions.

Step 2: Check for errors

Before proceeding, it’s important to check if there are any errors in the API response:

errors <- response$errors
if (length(errors) > 0) {
  stop("Errors")
}

If there are errors, the program will stop with an error message.

Step 3: Parse data from JSON as a data frame

Now that you have verified the API response, you can parse the data into a data frame:

data <- response$data

Step 4: Create a plot using ggplot2

Finally, you will use the ggplot2 package to create a polar bar plot of the global distribution of sequences by region:

library(ggplot2)


ggplot(
  data,
  aes(x = "", y = count, fill = region)) +
  geom_bar(width = 1, stat = "identity") +
  coord_polar("y", start = 0) +
  theme_minimal() +
  theme(
    panel.grid=element_blank(),
    panel.border = element_blank(),
    axis.ticks = element_blank(),
    axis.title.x = element_blank(),
    axis.title.y = element_blank(),
    axis.text.x = element_blank())

This will generate a polar bar plot displaying the global distribution of all sequences by region.