"binning" rows into ranges (dplyr/R)

Question

I am having a lot of difficulty trying to place rows from a dataset into "bins". For example, suppose I have a data frame "df" with "var1" and "var2" :

I want to create a new variable called "var3" that follows this logic (R code):

1) if var1 <5 and var2<5 .... then var3 = "a"
2) if var1 between (5,10) and var2 between (5,10) .... then var3 = "b"
3) if var1 > 10 and and var2>10 .... then var3 = "c"

From a previous question I posted (If statements with multiple ranges (R)), I tried the following logic:

library(dplyr)
df %>%
  mutate(var3 = case_when(var1 < 5 & var2 < 5 ~ 'a', 
                          var1 > 5 & var1 < 10 & var2 > 5 & var2 < 10 ~ 'b', 
                          var1 >10 & var2 >10 ~ 'c'))

But when I inspect the df$var3, the logic does not seem to be correct (i.e. some entries for var3 do not have any values. note: the smallest possible value of var1 and va2 is 0).

Can someone please help me?

Thanks

UPDATE:

Sample dataset:

a <- rnorm(50,10,10)
b <- rnorm(50, 2,8)

var1 = abs(a)
var2 = abs(b)

df = data.frame(var1, var2)

Answer 1

try this

library(dplyr)

set.seed(123)
df <- data.frame(var1 = round(runif(100)*20, 0),
                   var2 = round(runif(100)*20, 0))

df <- df %>% mutate(var3 = ifelse(var1 <= 5 & var2 <= 5, "a", ifelse(var1 <= 10 & var2 <= 10, "b", "c"))) 

to check

library(ggplot2)

df %>%
  ggplot() + geom_point(aes(x=var1, y= var2, color= var3))

Answer 2

If you want to use case_when,

library(dplyr)

## data make
set.seed(111)
df = data.frame(var1 = abs(rnorm(50,10,10)), var2 = abs(rnorm(50,2,8)))

## core
df <- df %>%
  mutate(var3 = case_when(var1 < 5 & var2 < 5 ~ 'a', 
                          var1 < 10 & var2 < 10 ~ 'b',
                          TRUE ~ 'c'))
## plot to check
with(df, plot(var1, var2, col = c(2:4)[as.numeric(as.factor(var3))], cex = 0.7))
abline(h = c(5, 10), v = c(5, 10), lty = 2)