Dealing with Timeseries data set that has not AM/PM and convert to 24 hrs format in R

Question

Let my time series data be

df <- data.frame(timestamp = c('2021-08-11 12:00:00', '2021-08-11 01:00:00', '2021-08-11 02:00:00', '2021-08-11 03:00:00', '2021-08-11 04:00:00', '2021-08-11 05:00:00', '2021-08-11 06:00:00', '2021-08-11 07:00:00', '2021-08-11 08:00:00', '2021-08-11 09:00:00', '2021-08-11 10:00:00', '2021-08-11 11:00:00', '2021-08-11 12:00:00', '2021-08-11 01:00:00', '2021-08-11 02:00:00', '2021-08-11 03:00:00', '2021-08-11 04:00:00', '2021-08-11 05:00:00', '2021-08-11 06:00:00', '2021-08-11 07:00:00', '2021-08-11 08:00:00', '2021-08-11 09:00:00', '2021-08-11 10:00:00', '2021-08-11 11:00:00' ),
value = c(77,190,17,-4,163,158,25,-2,132,119,-35,165,99,-21,199,62,-1,30,123,42,56,-36,123,24))

My requirement data frame

df <- data.frame(timestamp = c('2021-08-11 00:00:00', '2021-08-11 01:00:00', '2021-08-11 02:00:00', '2021-08-11 03:00:00', '2021-08-11 04:00:00', '2021-08-11 05:00:00', '2021-08-11 06:00:00', '2021-08-11 07:00:00', '2021-08-11 08:00:00', '2021-08-11 09:00:00', '2021-08-11 10:00:00', '2021-08-11 11:00:00', '2021-08-11 12:00:00', '2021-08-11 13:00:00', '2021-08-11 14:00:00', '2021-08-11 15:00:00', '2021-08-11 16:00:00', '2021-08-11 17:00:00', '2021-08-11 18:00:00', '2021-08-11 19:00:00', '2021-08-11 20:00:00', '2021-08-11 21:00:00', '2021-08-11 22:00:00', '2021-08-11 23:00:00' ),
                 value = c(77,190,17,-4,163,158,25,-2,132,119,-35,165,99,-21,199,62,-1,30,123,42,56,-36,123,24))

The original data is of the interval per minute or per second.

here the first

df$timestamp[1] = [1] "2021-08-11 12:00:00" 

is of AM, i.e. 00 hrs after night.

I want to convert the timestamp column to 24 hours format.

I want to have my timestamp like this

Answer 1

A tidyverse option.

library(tidyverse)

df %>%
  mutate(id = str_sub(timestamp, 1, 10),
         timestamp = ymd_hms(timestamp)) %>%
  group_by(id) %>%
  mutate(timestamp = date(timestamp)+hours(row_number()-1)) %>%
  ungroup() %>%
  select(-id)
  
# # A tibble: 24 x 2
#     timestamp           value
#     <dttm>              <dbl>
#  1  2021-08-11 00:00:00    77
#  2  2021-08-11 01:00:00   190
#  3  2021-08-11 02:00:00    17
#  4  2021-08-11 03:00:00    -4
#  5  2021-08-11 04:00:00   163
#  6  2021-08-11 05:00:00   158
#  7  2021-08-11 06:00:00    25
#  8  2021-08-11 07:00:00    -2
#  9  2021-08-11 08:00:00   132
# 10  2021-08-11 09:00:00   119
# # … with 14 more rows