collapse (version 1.0.0)

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, ...)

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

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

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

# S3 method for grouped_df
ffirst(x, TRA = NULL, na.rm = TRUE,
       use.g.names = FALSE, keep.group_vars = TRUE, ...)
# S3 method for 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 tibble (dplyr::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 - "*". See TRA.

na.rm

logical. Skip missing values and choose 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

make group-names and add to the result as names (vector method) or row-names (matrix and data.frame method). No row-names are generated for data.tables and grouped tibbles.

drop

matrix and data.frame method: drop dimensions and return 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, ...

See Also

Fast Statistical Functions, Collapse Overview

Examples

# NOT RUN {
## 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 tibbles - for use with dplyr
library(dplyr)
airquality %>% group_by(Month) %>% ffirst
airquality %>% group_by(Month) %>% select(Ozone) %>% ffirst(na.rm = FALSE)

# Note: All examples generalize to flast!
# }