If, else if and else syntax within for loop in R

Question

This is the sample dataframe I'm working with:

numbers <- data.frame(value=c(-5000,1,2,100,200,300,400,500, 1000, 2000, 10000, 12000))

I'm looking to create a new column in this data frame called "output" that contains values as follows:
-Same value as in column "value" if value between 1 and 10000
-10000 if the value in column "value" is more than 10000 and
-1 if the value in column "value" is less than 1

Desired output in the new column "output": 1,1,2,100,200,300,400,500, 1000,2000, 10000, 10000.

I would really like to learn how to use for loop, if, else if and else statements to get this output and have tried the following:

for (i in 1:nrow (numbers$value)){
  if (numbers$value[i] >10000){
    numbers$output <- 10000)
  } else if (numbers$value[i] < 1){
    numbers$output <- 1)
  } else {
    numbers$output <- numbers$value)
  }
}

Unfortunately, this gives me an error, Error: unexpected '}' in "}"

Appreciate your help in fixing this code!

This is not the question, but I suggest to consider case_when in cases with more then two if. library(dplyr) numbers %>% mutate(newCol = case_when(between(value, 1,10000) ~ value, value > 10000 ~ 10000, value < 1 ~ 1)) — TarJae
– TarJae, Commented Dec 4, 2021 at 6:14

tlhenvironment · Accepted Answer · 2021-12-04 05:04:26Z

4

I see why you are trying to solve this problem with a for loop (I have been there..). In R, there is a useful thing called vectorization. You can use the *apply family to apply a function over an input vector. By this, you give the function an input, and you automatically get an output of the same length.

sapply(numbers$value, function(x){
  if (x >10000) return(10000)
  else if (x < 1) return(1)
  else return(x)
}) -> numbers$output

answered Dec 4, 2021 at 5:04

tlhenvironment

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3 Comments

Rlearner Over a year ago

Thanks so much! This works great.

Rlearner Over a year ago

As a follow up, can I ask how I could replicate this code for multiple columns in the same dataframe. Example dataframe: numbersnew <- data.frame(value1=c(-5000,1,2,100,200,300,400,500, 1000, 2000, 10000, 12000), value2= c(-4000, 3,4, 150, 250, 350, 450, 550, 1050, 2050, 10050, 12050))

Jim Over a year ago

purrr.tidyverse.org/reference/map_if.html - map_if will let you choose columns to apply the function to

Dave2e · Accepted Answer · 2021-12-04 05:07:12Z

4

There are several errors in the original code: Not initializing the output variable, unmatched and unneeded ")", not using subscripts when necessary, and other errors. See the corrected code below.

numbers <- data.frame(value=c(-5000,1,2,100,200,300,400,500, 1000, 2000, 10000, 12000))
numbers$output<-NA
for (i in 1:nrow(numbers)){
   if (numbers$value[i] >10000){
      numbers$output[i] <- 10000
   } else if (numbers$value[i] < 1){
      numbers$output[i] <- 1
   } else {
      numbers$output[i] <- numbers$value[i]
   }
}
numbers

Here is a solution more straight forward using the case_when function from the dplyr package:

numbers <- data.frame(value=c(-5000,1,2,100,200,300,400,500, 1000, 2000, 10000, 12000))
library(dplyr)
numbers$output <-case_when(
   numbers$value >10000 ~ 10000,
   numbers$value < 1 ~ 1,
   TRUE ~ numbers$value. #default case
)
numbers

answered Dec 4, 2021 at 5:07

Dave2e

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1 Comment

Rlearner Over a year ago

Thanks so much for correcting the code and offering another solution! Appreciate it

D.J · Accepted Answer · 2021-12-04 05:52:09Z

1

in the spirit of ifelse-ness you could also use the ifelse() function.

numbers$output <- ifelse(numbers$value > 1000, 1000, ifelse(numbers$value < 0, 1, numbers$value))

answered Dec 4, 2021 at 5:52

D.J

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2 Comments

Jim Over a year ago

ifelse(number$value, < 1, -1, min(number$value, 10000))

D.J Over a year ago

smart, still a comma too much

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