collapse: ffirst_flast – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

ffirst_flast

Fast (Grouped) First and Last Value for Matrix-Like Objects

Description

ffirst and flast are S3 generic functions that (column-wise) returns the first and last values in x, (optionally) grouped by g. The TRA argument can further be used to transform x using its (groupwise) first and last values.

Usage

ffirst(x, ...)
flast(x, ...)

## Default S3 method:
ffirst(x, g = NULL, TRA = NULL, na.rm = TRUE,
       use.g.names = TRUE, ...)
## Default S3 method:
flast(x, g = NULL, TRA = NULL, na.rm = TRUE,
      use.g.names = TRUE, ...)

## S3 method for class 'matrix'
ffirst(x, g = NULL, TRA = NULL, na.rm = TRUE,
       use.g.names = TRUE, drop = TRUE, ...)
## S3 method for class 'matrix'
flast(x, g = NULL, TRA = NULL, na.rm = TRUE,
      use.g.names = TRUE, drop = TRUE, ...)

## S3 method for class 'data.frame'
ffirst(x, g = NULL, TRA = NULL, na.rm = TRUE,
       use.g.names = TRUE, drop = TRUE, ...)
## S3 method for class 'data.frame'
flast(x, g = NULL, TRA = NULL, na.rm = TRUE,
      use.g.names = TRUE, drop = TRUE, ...)

## S3 method for class 'grouped_df'
ffirst(x, TRA = NULL, na.rm = TRUE,
       use.g.names = FALSE, keep.group_vars = TRUE, ...)
## S3 method for class 'grouped_df'
flast(x, TRA = NULL, na.rm = TRUE,
      use.g.names = FALSE, keep.group_vars = TRUE, ...)

Arguments

`x`	a vector, matrix, data frame or grouped data frame (class 'grouped_df').
`g`	a factor, `GRP` object, atomic vector (internally converted to factor) or a list of vectors / factors (internally converted to a `GRP` object) used to group `x`.
`TRA`	an integer or quoted operator indicating the transformation to perform: 1 - "replace_fill" \| 2 - "replace" \| 3 - "-" \| 4 - "-+" \| 5 - "/" \| 6 - "%" \| 7 - "+" \| 8 - "*" \| 9 - "%%" \| 10 - "-%%". See `TRA`.
`na.rm`	logical. `TRUE` skips missing values and returns the first / last non-missing value i.e. if the first (1) / last (n) value is `NA`, take the second (2) / second-to-last (n-1) value etc..
`use.g.names`	logical. Make group-names and add to the result as names (default method) or row-names (matrix and data frame methods). No row-names are generated for data.table's.
`drop`	matrix and data.frame method: Logical. `TRUE` drops dimensions and returns an atomic vector if `g = NULL` and `TRA = NULL`.
`keep.group_vars`	grouped_df method: Logical. `FALSE` removes grouping variables after computation.
`...`	arguments to be passed to or from other methods.

Value

ffirst returns the first value in x, grouped by g, or (if TRA is used) x transformed by its first value, grouped by g. Similarly flast returns the last value in x, ...

Examples

## default vector method
ffirst(airquality$Ozone)                   # Simple first value
ffirst(airquality$Ozone, airquality$Month) # Grouped first value
ffirst(airquality$Ozone, airquality$Month,
       na.rm = FALSE)                      # Grouped first, but without skipping initial NA's

## data.frame method
ffirst(airquality)
ffirst(airquality, airquality$Month)
ffirst(airquality, airquality$Month, na.rm = FALSE) # Again first Ozone measurement in month 6 is NA

## matrix method
aqm <- qM(airquality)
ffirst(aqm)
ffirst(aqm, airquality$Month) # etc..
 
## method for grouped data frames - created with dplyr::group_by or fgroup_by
library(dplyr)
airquality %>% group_by(Month) %>% ffirst
airquality %>% group_by(Month) %>% select(Ozone) %>% ffirst(na.rm = FALSE)

# Note: All examples generalize to flast.

collapse

Advanced and Fast Data Transformation

v1.5.3

GPL (>= 2) | file LICENSE

Authors

Sebastian Krantz [aut, cre], Matt Dowle [ctb], Arun Srinivasan [ctb], Laurent Berge [ctb], Dirk Eddelbuettel [ctb], Josh Pasek [ctb], Kevin Tappe [ctb], R Core Team and contributors worldwide [ctb], Martyn Plummer [cph], 1999-2016 The R Core Team [cph]

Initial release

2021-03-05