r loop only returns one dataframe

I have a data structure like so:

I want to coalesce the column titles to the day numbers into a new column, then stack the first 70 rows of each column into 1 new column.

daynum = c("day1", "day2", "day3", "day4")
year1 = c(1,2,3,4)
year2 = c(5,6,7,8)
year3 = c(7,8,9,10)

df <- data.frame(daynum, year1, year2, year3)
print(df)

  #create output data outside of loop
summerdata = data.frame()

for (i in names(df[,-1])){
  yeardate = data.frame(paste(i, df$daynum, sep="-"))
  sdata = data.frame(df[[i]])
  sur = sdata[1:70,]
  sy = yeardate[1:70,]
  endsummers = cbind(sy,sur)
  summerdata = rbind(summerdata,endsummers)
}
colnames(endsummers)=c("yeardate","summertemp")
print(endsummers)  

all that returns in the first year1, and it’s storing the numbers as text.

output should look like this:

      yeardate       summertemp
 [1,] "year1-day1"  85      
 [2,] "year1-day2"  87     
 [3,] "year1-day3"  79  

>Solution :

library(tidyverse)
df %>%
  pivot_longer(-daynum) %>%
  group_by(name) %>% slice(1:70) %>% ungroup() %>%  # only first 70 rows per year
  unite("daynum", 2:1, sep = "-") %>%
  arrange(daynum)

Result

# A tibble: 12 × 2
   daynum     value
   <chr>      <dbl>
 1 year1-day1     1
 2 year1-day2     2
 3 year1-day3     3
 4 year1-day4     4
 5 year2-day1     5
 6 year2-day2     6
 7 year2-day3     7
 8 year2-day4     8
 9 year3-day1     7
10 year3-day2     8
11 year3-day3     9
12 year3-day4    10