mutate_rows: mutate selected rows

In skranz/dplyrExtras: extra functionality for dplyr like mutate_rows for mutation of a subset of rows

Description

change values of columns only in rows that satisfy the .if condition Note: you cannot create new columns with mutate_rows but only change values in selected rows of existing columns

Usage

mutate_rows(.data, .if, ...)

Arguments

.data	the data
.if	a logical condition that selects rows, e.g. a=="B"
...	the command to mutate existing columns

Examples

## Not run: 
  library(microbenchmark)
  library(dplyr)
  library(data.table)
  library(dplyrExtras)

  # create a data
  set.seed(123456)
  n = 10
  df = data.frame(a= sample(1:3,n,replace=TRUE),
  b= sample(1:100,n,replace=TRUE),
  x=rnorm(n))
  dt = as.data.table(df)
  
  # different calls to mutate_rows
  mutate_rows(df,a==3,y=100)
  mutate_rows(tbl_df(df),a==1,x=200)
  mutate_rows(as.tbl(df),a==1,x=300,b=400)
  mutate_rows(dt,a==1 | a==2,x=400)
  mutate_rows(group_by(dt,a),a==1 | a==2,x=mean(b)) 
  mutate_rows(group_by(df,a),a==1 | a==2,x=mean(b))

  # if you create a new column rows that don't
  # match the if condition have an NA
  mutate_rows(df,a==3,z=100)
  
  # You can only have one if condition in a mutate_rows call
  # So multiple changes require nesting or piping
  library(magrittr)
  df 
         mutate_rows(a==2,z=200) 
  
  # For historical reasons there is also still the synonym
  # mutate_if. But not that dplyr 5.0 has introduced its own
  # mutate_if function with quite different functionality
  
  mutate_if(df,a==3,y=99)
  
    
  
  # Small benchmark: compare with mutate + ifelse
  n = 1e6
  df = data.frame(a= sample(1:3,n,replace=TRUE),
  b= sample(1:100,n,replace=TRUE),
  x=rnorm(n))
  microbenchmark(times = 5L,
    mutate(df, x=ifelse(a==2,x+100,x)),
    mutate(df, x=if_else(a==2,x+100,x)),
    mutate_rows(df, a==2, x=x+100)
  )
#             mean
# ifelse      540.7145
# if_else     360.4928
# mutate_rows 114.3891

## End(Not run)

skranz/dplyrExtras documentation built on May 20, 2020, 6:39 p.m.