I have a dataframe df1 that summarizes different observations of an individual ID overtime but rounded at fixed 45-minutes intervals starting at 00:00:00 (00:00:00, 00:45:00, etc.). As an example:

df1<- data.frame(DateTime45=c("2017-07-09 00:00:00","2017-07-09 00:45:00","2017-07-09 02:15:00","2017-07-09 03:45:00"),
                 ID=c("A","A","A","A"),
                 VariableX=c(0,2,0,4))

df1
           DateTime45 ID VariableX
1 2017-07-09 00:00:00  A         0
2 2017-07-09 00:45:00  A         2
3 2017-07-09 02:15:00  A         0
4 2017-07-09 03:45:00  A         4

I have another dataframe df2 in which I have other info (vedba) about this individual also overtime, but in this case without 45-minutes time intervals. As an example:

df2<- data.frame(DateTime= c("2017-07-08 23:40:57.245","2017-07-08 23:58:12.945","2017-07-09 00:01:00.345","2017-07-09 00:07:12.845","2017-07-09 00:28:34.845","2017-07-09 00:31:46.567","2017-07-09 00:53:21.345","2017-07-09 01:01:34.545","2017-07-09 01:09:12.246","2017-07-09 01:23:12.321","2017-07-09 01:34:26.687","2017-07-09 01:57:08.687","2017-07-09 02:05:23.789","2017-07-09 02:32:24.789","2017-07-09 02:42:34.536","2017-07-09 02:59:00.098","2017-07-09 03:03:01.434","2017-07-09 03:11:38.987","2017-07-09 03:23:31.345","2017-07-09 03:28:21.345","2017-07-09 03:42:53.345"),
                 ID=c("A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A"),
                 vedba=c(1.87,2.3,0.3,0.67,1.3,2.1,3.6,0.1,0.8,1.3,2.4,1.5,1.23,2.02,1.89,0.78,1.11,2.13,1.20,0.34,0.94))
df2$DateTime<- as.POSIXct(df2$DateTime, format="%Y-%m-%d %H:%M:%OS",tz="UTC")

df2

                  DateTime ID vedba
1  2017-07-08 23:40:57.244  A  1.87
2  2017-07-08 23:58:12.944  A  2.30
3  2017-07-09 00:01:00.345  A  0.30
4  2017-07-09 00:07:12.845  A  0.67
.        .          .       .    .
.        .          .       .    .

I want to calculate for each row in df1, the mean vedba using values from df2. The key is that I want to consider that for each time in df1, the window encompasses between 22 minutes and 30 seconds before and after (that is, df1$DateTime45 is the central value of the range). For instance, the time-range for df1[1,1] (2017-07-09 00:00:00) is between 2017-07-08 23:37:30 and 2017-07-09 00:22:30.

In this example, I would expect to get this:

df3
           DateTime45 ID VariableX meanVedba n_vedba
1 2017-07-09 00:00:00  A         0 1.2850000       4
2 2017-07-09 00:45:00  A         2 1.7750000       4
3 2017-07-09 02:15:00  A         0 1.5833333       3
4 2017-07-09 03:45:00  A         4 0.8266667       3

*Note: I include an n_vedba variable to check if the code is taking the right number of rows from df2.

My try was this code:

setDT(df1)[, DateTime45 := ymd_hms(DateTime45)]
setDT(df2)[, dt_floor := round_date(ymd_hms(DateTime), unit = "45 mins")]
df3<- df2[df1, .(meanVedba = mean(vedba), 
                                                  n_vedba=.N),
                        on = .(ID, dt_floor = DateTime45), by = .EACHI]

df3

   ID            dt_floor meanVedba n_vedba
1:  A 2017-07-09 00:00:00 0.4850000       2
2:  A 2017-07-09 00:45:00 2.3333333       3
3:  A 2017-07-09 02:15:00        NA       0
4:  A 2017-07-09 03:45:00 0.8266667       3

However, as you can see, I don't get what I would expect.

Does anyone know why and how to change the code in order to accomplish what I want?

Extra comment

When I have hour-intervals instead of 45-minutes intervals the code I showed works.

1. I create the dataframes

df1<- data.frame(DateTime=c("2017-07-09 00:00:00","2017-07-09 01:00:00","2017-07-09 02:00:00","2017-07-09 03:00:00","2017-07-09 04:00:00"),
                 ID=c("A","A","A","A","A"),
                 VariableX=c(0,2,0,4,7))
df1$DateTime<- as.POSIXct(df1$DateTime45, format="%Y-%m-%d %H:%M:%S",tz="UTC")
df1

             DateTime ID VariableX
1 2017-07-09 00:00:00  A         0
2 2017-07-09 01:00:00  A         2
3 2017-07-09 02:00:00  A         0
4 2017-07-09 03:00:00  A         4
5 2017-07-09 04:00:00  A         7

df2<- data.frame(DateTime= c("2017-07-08 23:40:57.245","2017-07-08 23:58:12.945","2017-07-09 00:01:00.345","2017-07-09 00:07:12.845","2017-07-09 00:28:34.845","2017-07-09 00:31:46.567","2017-07-09 00:53:21.345","2017-07-09 01:01:34.545","2017-07-09 01:09:12.246","2017-07-09 01:23:12.321","2017-07-09 01:34:26.687","2017-07-09 01:57:08.687","2017-07-09 02:05:23.789","2017-07-09 02:32:24.789","2017-07-09 02:42:34.536","2017-07-09 02:59:00.098","2017-07-09 03:03:01.434","2017-07-09 03:11:38.987","2017-07-09 03:23:31.345","2017-07-09 03:28:21.345","2017-07-09 03:42:53.345"),
                 ID=c("A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A","A"),
                 vedba=c(1.87,2.3,0.3,0.67,1.3,2.1,3.6,0.1,0.8,1.3,2.4,1.5,1.23,2.02,1.89,0.78,1.11,2.13,1.20,0.34,0.94))
df2$DateTime<- as.POSIXct(df2$DateTime, format="%Y-%m-%d %H:%M:%OS",tz="UTC")

df2

               DateTime ID vedba            dt_floor
 1: 2017-07-08 23:40:57  A  1.87 2017-07-09 00:00:00
 2: 2017-07-08 23:58:12  A  2.30 2017-07-09 00:00:00
 3: 2017-07-09 00:01:00  A  0.30 2017-07-09 00:00:00
 4: 2017-07-09 00:07:12  A  0.67 2017-07-09 00:00:00
 .            .          .    .            .
 .            .          .    .            .

2. I calculate vedba for hourly-bin intervals

setDT(df1)[, DateTime45 := ymd_hms(DateTime)]
setDT(df2)[, dt_floor := round_date(ymd_hms(DateTime), unit = "hour")]
df3<- df2[df1, .(meanVedba = mean(vedba), 
                                                  n_vedba=.N),
                        on = .(ID, dt_floor = DateTime), by = .EACHI]

df3

   ID            dt_floor meanVedba n_vedba
1:  A 2017-07-09 00:00:00  1.288000       5
2:  A 2017-07-09 01:00:00  1.580000       5
3:  A 2017-07-09 02:00:00  1.710000       3
4:  A 2017-07-09 03:00:00  1.352857       7
5:  A 2017-07-09 04:00:00  0.940000       1