Conditionally Count in dplyr

Try

 library(dplyr)
 memberorders %>% 
        group_by(MemID) %>% 
        summarise(sum2= sum(value[week<=2]), sum4= sum(value[week <=4]), 
                  count2=sum(week<=2), count4= sum(week<=4))

Using both previous ideas and keeping it consistent:

library(tidyverse)

MemberLTV_2 <- memberorders %>%
  group_by(MemID) %>%
    summarize(
      count2 = length(value[week<=2]),
      count4 = length(value[week<=4]),
      sum2 = sum(value[week<=2]),
      sum4 = sum(value[week<=4])
      )