The dataset:

Date
2021-09-25T17:07:24.222Z    
2021-09-25T16:17:20.376Z
2021-09-24T09:30:53.013Z
2021-09-24T09:06:24.565Z

I would like to count the number of rows per day. For example, 2021-09-25 will be 2.

To solve said challenge I looked at the following post:

• Count and Aggregate Date in R

The answer of Rorshach is the solution. However, I do not understand how I can format my rows in the Date column to 2021/09/24 instead of 2021-09-24T09:06:24.565Z.

Could someone explain to me how to format the entries in the Date column?

CodePudding user response：

After converting the date you may use table to count occurrence of each Date.

table(as.Date(df$Date))

#2021-09-24 2021-09-25 
#         2          2 

CodePudding user response：

Parse the string into a datetime object and then extract the date (without the hours and minutes) to be able to count:

library(dplyr)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union

tibble::tribble(
  ~Date,
  "2021-09-25T17:07:24.222Z",
  "2021-09-25T16:17:20.376Z",
  "2021-09-24T09:30:53.013Z",
  "2021-09-24T09:06:24.565Z"
) %>%
  mutate(
    day = Date %>% parse_datetime() %>% as.Date()
  ) %>%
  count(day)
#> # A tibble: 2 × 2
#>   day            n
#>   <date>     <int>
#> 1 2021-09-24     2
#> 2 2021-09-25     2

CodePudding user response：

@RonakShah's answer is good, but to have the dataframe in better format, use the count function from the plyr library:

library(plyr)
count(as.Date(df$Date))

Output:

           x freq
1 2021-09-24    2
2 2021-09-25    2