R：当 max <= min 时，如何替换（切换）数据帧中一行中的最大值和最小值？

Question

How we can replace(switch) the max and min values in each row in this dataframe ONLY if max <= min ?

> my_data

   year month day   max      min
1  2019     1   1   20.4   -24.4
2  2019     1   2   12.9   -20.4
3  2019     1   3  -27.1    10.3
4  2019     1   4  -20.8    11.0
5  2019     1   5  -16.2    -8.9

The result should be like this:

> my_data

   year month day   max      min
1  2019     1   1   20.4   -24.4
2  2019     1   2   12.9   -20.4
3  2019     1   3   10.3   -27.1
4  2019     1   4   11.0   -20.8
5  2019     1   5   -8.9   -16.2

Thanks in advance.

Answer 1

One option is pmax/pmin

library(dplyr)
my_data %>% 
    mutate(maxnew =  pmax(max, min), minnew = pmin(max, min))  %>%
    select(year, month, day, max = maxnew, min = minnew)
#  year month day  max   min
#1 2019     1   1 20.4 -24.4
#2 2019     1   2 12.9 -20.4
#3 2019     1   3 10.3 -27.1
#4 2019     1   4 11.0 -20.8
#5 2019     1   5 -8.9 -16.2

---

Or a compact way is with base R

nm1 <- c('max', 'min')
my_data[nm1] <- t(apply(my_data[nm1], 1, sort))[, 2:1]

---

Or using pmax/pmin

my_data[nm1] <- lapply(list(pmax, pmin), function(f) do.call(f, my_data[nm1]))

data

my_data <- structure(list(year = c(2019L, 2019L, 2019L, 2019L, 2019L), month = c(1L, 
1L, 1L, 1L, 1L), day = 1:5, max = c(20.4, 12.9, -27.1, -20.8, 
-16.2), min = c(-24.4, -20.4, 10.3, 11, -8.9)), 
class = "data.frame", row.names = c("1", 
"2", "3", "4", "5"))

Answer 2

We can find the index where max is less than min . Store those max values in temporary variable and then swap the max and min values using that.

inds <- df$max < df$min
temp <- df$max[inds]
df$max[inds] <- df$min[inds]
df$min[inds] <- temp
df

#  year month day  max   min
#1 2019     1   1 20.4 -24.4
#2 2019     1   2 12.9 -20.4
#3 2019     1   3 10.3 -27.1
#4 2019     1   4 11.0 -20.8
#5 2019     1   5 -8.9 -16.2

data

df <- structure(list(year = c(2019L, 2019L, 2019L, 2019L, 2019L), month = c(1L, 
1L, 1L, 1L, 1L), day = 1:5, max = c(20.4, 12.9, -27.1, -20.8, 
-16.2), min = c(-24.4, -20.4, 10.3, 11, -8.9)), class = "data.frame", 
row.names = c("1", "2", "3", "4", "5"))