Create a function in R to compare rows

Question

I want to create a function in R to compare “Current Row Value” and “Previous Row Value. a. If Current Row Value is lower than Previous Row Value then return word LOW b. If Current Row Value is higher than Previous Value then return word HIGH c. If Current Row Value is same as Previous Row Value then return word EQUAL

I want to create a new COLUMN named Decision where the words would be stored like below

Value Decision

1 N/A

2 HIGH

1.5 LOW

1.4 LOW

1.4 EQUAL

akrun akrun · Accepted Answer · 2020-03-28T20:11:17

We can use case_when to compare the 'Value' with the previous 'Value' (lag) and create the column 'Decision' based on whether it is lower or higher

library(dplyr)
df1 %>%
 mutate(Decision = case_when(Value < lag(Value) ~ "LOW", 
     Value > lag(Value) ~ "HIGH", Value == lag(Value) ~ "EQUAL"))
#  Value Decision
#1   1.0     <NA>
#2   2.0     HIGH
#3   1.5      LOW
#4   1.4      LOW
#5   1.4    EQUAL

Or another option is to take the difference and then change the labels in factor

with(df1, c(NA_character_, 
    as.character(factor(sign(Value[-length(Value)] - Value[-1]),         
       levels = c(-1, 1, 0), labels = c("HIGH", "LOW", "EQUAL")))))
#[1] NA      "HIGH"  "LOW"   "LOW"   "EQUAL"

Or using a for loop

df1$Decision <- rep(NA_character_, nrow(df1))
for(i in 2: nrow(df1)){
    if(df1$Value[i] > df1$Value[i-1]){
       df1$Decision[i] <- "HIGH"
      } else if(df1$Value[i] < df1$Value[i-1]) {

        df1$Decision[i] <- "LOW"
       } else df1$Decision[i] <- "EQUAL"


   }

If it needs to be a function

f1 <- function(dat, colNm, newCol) {
  dat[[newCol]] <- rep(NA_character_, nrow(dat))
    for(i in 2: nrow(dat)){
        if(dat[[colNm]][i] > dat[[colNm]][i-1]){
           dat[[newCol]][i] <- "HIGH"
          } else if(dat[[colNm]][i] < dat[[colNm]][i-1]) {

            dat[[newCol]][i] <- "LOW"
           } else dat[[newCol]][i] <- "EQUAL"


       }
     dat
   }

f1(df1, "Value", "Decision")

data

df1 <- structure(list(Value = c(1, 2, 1.5, 1.4, 1.4)), class = "data.frame",
     row.names = c(NA, 
-5L))

Create a function in R to compare rows

1 Answers

data