For loop in R doesn't go through all values

I need to go through all years and define new days by the starting hour. My code right now looks like this:

starting_hour <- 5
hours_in_day <- 48

for (x in unique(data$Year)) {
  a = 1
  while (a <= nrow(filter(data, data$Year == x)) && (data$Year == x)) {
    if ((data[a, "Hours"] == starting_hour) && (a < 48)) {
      for (c in 1:floor((nrow(filter(data, data$Year == x))-starting_hour)/hours_in_day)) {
        for (b in 0:(hours_in_day-1)) {
          data[a, "Hours"] <- b
          data[a, "Date"] <- c
          a <- a+1
        }
      }
      next
    }
    else {
      data[a, "Date"] <- 0
      a <- a+1
      if (data[a, "Year"] != x) {
        break
      }
      next
    }
  }
}`

Right now this only works with the first year. I don't understand why it doesn't go through all years. Here's first 50 rows of my data:

> dput(data)
structure(list(Date = structure(c(1419984000, 1388534400, 1388534400, 
1388534400, 1388534400, 1388534400, 1388534400, 1388534400, 1388534400, 
1388534400, 1388534400, 1388534400, 1388534400, 1388534400, 1388534400, 
1388534400, 1388534400, 1388534400, 1388534400, 1388534400, 1388534400, 
1388534400, 1388534400, 1388534400, 1388534400, 1388620800, 1388620800, 
1388620800, 1388620800, 1388620800, 1388620800, 1388620800, 1388620800, 
1388620800, 1388620800, 1388620800, 1388620800, 1388620800, 1388620800, 
1388620800, 1388620800, 1388620800, 1388620800, 1388620800, 1388620800, 
1388620800, 1388620800, 1388620800, 1388620800, 1388707200), tzone = "UTC", class = c("POSIXct", 
"POSIXt")), Year = c(2014, 2014, 2014, 2014, 2014, 2014, 2014, 
2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 
2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 
2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 
2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014), 
    Hours = c(23, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 
    14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 0, 1, 2, 3, 4, 5, 
    6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 
    22, 23, 0)), row.names = c(NA, -50L), class = c("tbl_df", 
"tbl", "data.frame"))