根据r中的另一列更改一列的值

Question

I have the following data, and I want to change the values in the count column to negative if the text in 'Color' is Yellow. I tried mutate_if with no success. How can I go about doing so if I want to:

1. Replace the values in count with the new negative values, or
2. Create a new column with the name Count_final with new negative values, as well as the same old values for the entries that are not yellow?

Thank you.

data <- tibble::tribble(
    ~Color,    ~Item, ~Count,       ~Year,
    "Blue",    "Bag",     50, "2009-2011",
    "Blue", "Wallet",     60, "2009-2011",
   "Green",  "Shoes",     80, "2009-2011",
   "Green",  "Shirt",     90, "2009-2011",
  "Yellow", "Flower",     20, "2009-2011",
  "Yellow",   "Bees",     30, "2009-2011",
    "Blue",    "Bag",     50, "2009-2011",
    "Blue", "Wallet",     60, "2009-2011",
   "Green",  "Shoes",     90, "2009-2011",
   "Green",  "Shirt",     20, "2009-2011",
  "Yellow", "Flower",     10, "2009-2011",
  "Yellow",   "Bees",      5, "2009-2011"
  )

Answer 1

We can multiply Count with 1 (to keep the value as it is) if Color is not "Yellow" and -1 if Color is "Yellow" . This can be achieved directly with

data$Count_final <- with(data, Count * c(1, -1)[(Color == "Yellow") + 1])

# A tibble: 12 x 5
#   Color  Item   Count Year      Count_final
#   <chr>  <chr>  <dbl> <chr>           <dbl>
# 1 Blue   Bag       50 2009-2011          50
# 2 Blue   Wallet    60 2009-2011          60
# 3 Green  Shoes     80 2009-2011          80
# 4 Green  Shirt     90 2009-2011          90
# 5 Yellow Flower    20 2009-2011         -20
# 6 Yellow Bees      30 2009-2011         -30
# 7 Blue   Bag       50 2009-2011          50
# 8 Blue   Wallet    60 2009-2011          60
# 9 Green  Shoes     90 2009-2011          90
#10 Green  Shirt     20 2009-2011          20
#11 Yellow Flower    10 2009-2011         -10
#12 Yellow Bees       5 2009-2011          -5

Or with simple if_else

library(dplyr)
data %>% mutate(Count_final = Count * if_else(Color == "Yellow", -1, 1))

Or as @Kent Johnson suggested -

data %>% mutate(Count_final = if_else(Color=='Yellow', -Count, Count))