dplyr & tidyr essentials

# ── dplyr essentials ──────────────────────────────────────────
library(dplyr); library(tidyr)

# filter rows
iris |> filter(Species == "setosa", Sepal.Length > 5)

# select columns
iris |> select(Species, starts_with("Sepal"))

# mutate (add/transform columns)
iris |> mutate(sepal_ratio = Sepal.Length / Sepal.Width)

# group_by + summarise
iris |>
  group_by(Species) |>
  summarise(mean_SL = mean(Sepal.Length),
            sd_SL   = sd(Sepal.Length),
            n       = n())

# arrange
iris |> arrange(desc(Sepal.Length)) |> head(5)

# rename
iris |> rename(sp = Species)

# ── tidyr ──────────────────────────────────────────────────────
df <- data.frame(species = c("A","A","B","B"),
                 trait   = c("BL","BD","BL","BD"),
                 value   = c(10,5,8,4))

# pivot_wider (long → wide)
df |> pivot_wider(names_from = trait, values_from = value)

# pivot_longer (wide → long)
iris |> pivot_longer(cols = -Species, names_to = "trait", values_to = "value")

# drop_na / replace_na
iris |> drop_na()
iris |> replace_na(list(Sepal.Length = 0))

# left_join
sp_info <- data.frame(Species = c("setosa","versicolor","virginica"),
                      group   = c("A","B","B"))
iris |> left_join(sp_info, by = "Species") |> head(3)