How to get the output from the function in a column of a dataframe - R - r

Question

Hi I have a simple function:
same_picking <- function(cena){
data_model2$price_model2 <- 0.6 + cena * data_model2$item_SKU + 0.4
}
I would like the output to be rewritten in a column of a data.frame.
currently, because I still did not get the first writing of a function the column is still filled with NAs.. but I would like that after every run of a function the values would be rewriten in theat column.
count_code sifra item_SKU price_model2
281 0421 2 NA
683 0499 5 NA
903 0654 3 NA
7390 0942 3 NA
2778 0796 5 NA
2778 0796 7 NA
7066 0907 83 NA
281 0421 2 NA
I have tried with the comands: data.frame and within... but it got me nowhere.
I would appraciate the help.
Andraz
Solution:
same_picking <- function(cena){
data_model2$price_model2 <<- 0.6 + cena * data_model2$item_SKU + 0.4
}
<<- operator allows you to access the object from the ouside. Very clean :)

Answer 1

The simplest way would be to return the df from function:
df <- read.table(
text = "count_code sifra item_SKU price_model2
281 0421 2 NA
683 0499 5 NA
903 0654 3 NA
7390 0942 3 NA
2778 0796 5 NA
2778 0796 7 NA
7066 0907 83 NA
281 0421 2 NA",
header = TRUE)
head(df, 2)
# count_code sifra item_SKU price_model2
# 1 281 421 2 NA
# 2 683 499 5 NA
# 1st ---------------------------------------------------------------------
same_picking_1 <- function(df, cena){
df$price_model2 <- 0.6 + cena * df$item_SKU + 0.4
return(df)
}
df2 <- same_picking_1(df, 1)
head(df2, 2)
# count_code sifra item_SKU price_model2
# 1 281 421 2 3
# 2 683 499 5 6
Other options, data.table and dplyr:
same_picking_2 <- function(cena, item_SKU){
0.6 + cena * df$item_SKU + 0.4
}
# data.table --------------------------------------------------------------
library(data.table)
dt <- data.table(df)
dt[, price_model2 := same_picking_2(1, item_SKU)]
head(dt, 2)
# count_code sifra item_SKU price_model2
# 1: 281 421 2 3
# 2: 683 499 5 6
# dplyr -------------------------------------------------------------------
library(dplyr)
df3 <- df %>% mutate(price_model2 = same_picking_2(1, item_SKU))
head(df3, 2)
# count_code sifra item_SKU price_model2
# 1 281 421 2 3
# 2 683 499 5 6
Edit after OP comment:
You can also wrap data.table solution into a function
# data.table --------------------------------------------------------------
library(data.table)
same_picking_2_int <- function(cena, item_SKU){
0.6 + cena * df$item_SKU + 0.4
}
same_picking_2 <- function(dt, cena){
dt[, price_model2 := same_picking_2_int(cena, item_SKU)]
}
# Use update by reference
dt <- data.table(df)
head(dt, 2)
same_picking_2(dt, 1)
head(dt, 2)
# Slightly more readable, the same output, also utilizes the update by reference of data.table (see tracemem())
dt <- data.table(df)
tracemem(dt)
head(dt, 2)
dt <- same_picking_2(dt, 1)
head(dt, 2)