maditr: maditr: Pipe-Style Interface for 'data.table'

Description Examples

Description

Package provides pipe-style interface for data.table. It preserves all data.table features without significant impact on performance. 'let' and 'take' functions are simplified interfaces for most common data manipulation tasks.

Examples

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# examples form 'dplyr' package
data(mtcars)

# Newly created variables are available immediately
mtcars %>%
    let(
        cyl2 = cyl * 2,
        cyl4 = cyl2 * 2
    ) %>% head()

# You can also use let() to remove variables and
# modify existing variables
mtcars %>%
    let(
        mpg = NULL,
        disp = disp * 0.0163871 # convert to litres
    ) %>% head()


# window functions are useful for grouped computations
mtcars %>%
    let(rank = rank(-mpg, ties.method = "min"),
        by = cyl) %>%
    head()

# You can drop variables by setting them to NULL
mtcars %>%
    let(cyl = NULL) %>%
    head()

# keeps all existing variables
mtcars %>%
    let(displ_l = disp / 61.0237) %>%
    head()

# keeps only the variables you create
mtcars %>%
    take(displ_l = disp / 61.0237)


# can refer to both contextual variables and variable names:
var = 100
mtcars %>%
    let(cyl = cyl * var) %>%
    head()

# filter by condition
mtcars %>%
    take_if(am==0)

# filter by compound condition
mtcars %>%
    take_if(am==0 & mpg>mean(mpg))


# A 'take' with summary functions applied without 'by' argument returns an aggregated data
mtcars %>%
    take(mean = mean(disp), n = .N)

# Usually, you'll want to group first
mtcars %>%
    take(mean = mean(disp), n = .N, by = am)

# grouping by multiple variables
mtcars %>%
    take(mean = mean(disp), n = .N, by = list(am, vs))

# parametric evaluation:
var = quote(mean(cyl))
take(mtcars, eval(var))


# You can group by expressions:
mtcars %>%
    take(
        fun = mean,
        by = list(vsam = vs + am)
    )

hope-data-science/tidydt0 documentation built on Feb. 3, 2020, 12:04 a.m.