Deriving Quantiles or Percentiles in R

Percentiles can be calculated in R using the quantile function. The function has the argument type which allows for nine different percentile definitions to be used. The default is type = 7, which uses a piecewise-linear estimate of the cumulative distribution function to find percentiles.

This is how the 25th and 40th percentiles of aval could be calculated using the default type.

quantile(aval, probs = c(0.25, 0.4))
─ Session info ───────────────────────────────────────────────────────────────
 setting  value
 version  R version 4.4.2 (2024-10-31)
 os       Ubuntu 24.04.3 LTS
 system   x86_64, linux-gnu
 ui       X11
 language (EN)
 collate  C.UTF-8
 ctype    C.UTF-8
 tz       UTC
 date     2025-10-08
 pandoc   3.6.3 @ /opt/quarto/bin/tools/ (via rmarkdown)

─ Packages ───────────────────────────────────────────────────────────────────
 ! package     * version date (UTC) lib source
 P cli           3.6.3   2024-06-21 [?] RSPM (R 4.4.0)
 P digest        0.6.37  2024-08-19 [?] RSPM (R 4.4.0)
 P evaluate      1.0.0   2024-09-17 [?] RSPM (R 4.4.0)
 P fastmap       1.2.0   2024-05-15 [?] RSPM (R 4.4.0)
 P htmltools     0.5.8.1 2024-04-04 [?] RSPM (R 4.4.0)
 P htmlwidgets   1.6.4   2023-12-06 [?] RSPM (R 4.4.0)
 P jsonlite      1.8.9   2024-09-20 [?] RSPM (R 4.4.0)
 P knitr         1.50    2025-03-16 [?] RSPM (R 4.4.0)
   renv          1.0.10  2024-10-05 [1] RSPM (R 4.4.0)
 P rlang         1.1.6   2025-04-11 [?] RSPM (R 4.4.0)
 P rmarkdown     2.28    2024-08-17 [?] RSPM (R 4.4.0)
 P sessioninfo   1.2.2   2021-12-06 [?] RSPM (R 4.4.0)
 P xfun          0.52    2025-04-02 [?] RSPM (R 4.4.0)
 P yaml          2.3.10  2024-07-26 [?] RSPM (R 4.4.0)

 [1] /home/runner/work/CAMIS/CAMIS/renv/library/linux-ubuntu-noble/R-4.4/x86_64-pc-linux-gnu
 [2] /opt/R/4.4.2/lib/R/library

 P ── Loaded and on-disk path mismatch.

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