How to create a time series object yyyy-mm-dd hh:mm:ss?

Question

I am trying to convert sound data to a time-series object in order to analyse it further (using f.ex. WelchPSD from 'bspec' package). The frequency of my data is 25811 samples/second (Hz).

My sound file s2_d

> str(s2_d)
 int [1:52422753] -442 -434 -428 -413 -389 -386 -382 -387 -403 -373 ...

is an integer after I have extracted the data from the Wave object created by Waveread in package signal.

The file starts and ends:

> begin <- as.POSIXct("2017-08-17 17:04:34", tz="UTC")

> end <- as.POSIXct("2017-08-17 17:38:25", tz="UTC")

I have tried converting s2_d to ts with following lines:

> s2_dts <- ts(s2_d, start = as.numeric(begin), end = as.numeric(end), frequency = 25811)

> s2_dts <- as.ts(s2_d, start = as.numeric(begin), end = as.numeric(end), frequency = 25811)

> s2_dts <- ts(s2_d, start = as.numeric(as.POSIXct(begin)), end = as.numeric(as.POSIXct(end)), frequency = 25811)

> s2_dts <- as.ts(s2_d, start = as.numeric(as.POSIXct(begin)), end = as.numeric(as.POSIXct(end)), frequency = 25811)

They all convert s2_d to a ts

> class(s2_dts)
[1] "ts"
> start(s2_dts)
[1] 1502989474          1

but when I try the function window(), I can not extract f.ex. 1 second snippet out of my time series so something is not quite right.

> x <- window(s2_dts, start = as.numeric(begin), end = as.numeric("2017-08-17 17:04:35"), extend= TRUE)
Error in if (start > end) stop("'start' cannot be after 'end'") : 
  missing value where TRUE/FALSE needed
In addition: Warning message:
In window.default(x, ...) : NAs introduced by coercion

I finally tried:

> s2_dts <- ts(s2_d, start = c(2017,8,17,17,04,34), end = c(2017,8,17,17,38,25), frequency = 25811)

> start(s2_dts)
[1] 2017    8

> time(s2_dts)
Time Series:
Start = c(2017, 8) 
End = c(2017, 8) 
Frequency = 25811 [1] 2017

This is better evenif only year and month are recognised. How can I get the whole time including day, hour, minute and second to be the start time of the time series?

Any help will be greatly appreciated.

Be careful with the start argument inside ts, it expects a single number OR a vector of two integers. Using start(s2_dts) does not give year and month but the first 2 integers you gave inside ts. Read carefully the documentation of start argument : "the time of the first observation. Either a single number or a vector of two integers, which specify a natural time unit and a (1-based) number of samples into the time unit. See the examples for the use of the second form." — bVa
And use a correct end argument inside window to have a correct output : end = as.numeric(as.POSIXct("2017-08-17 17:04:35")), you forgot as.POSIXct(). @Outi — bVa
Thank you for your reply. I added as.POSIXCT() to end but do not still get the right answer. > head(s2_dts) [1] -0.02425873 -0.15219589 -0.39131684 -0.42728653 0.25058982 1.64021640 > head(x) [1] 0.32049328 0.35900218 0.01488998 0.51875873 1.69127310 1.55796914 > These two heads should be the same. — Outi
I have read the documentation of ts many times but do not understand how to give the start and end time in my case. As you can see in my answer, I have tried to change the date time Posixct object to a single number as said in the documentation. Can you give a suggestion how to do it @bVa? — Outi

bVa bVa · Accepted Answer · 2018-02-16T10:08:12

data <- runif(10, 1, 10) # mock data
> data
[1] 9.455453 4.596560 9.675503 7.437548 2.722311 7.729820 5.737903 2.540364 3.512660 5.555681

# 2 samples/second 
begin <- as.POSIXct("2017-08-17 17:04:34", tz="UTC")
end <- as.POSIXct("2017-08-17 17:04:39", tz="UTC")

# Create time-series object
df_ts <- ts(data, 
            start = as.numeric(begin), 
            end = as.numeric(end), 
            frequency = 2)

> window(df_ts, 
         start = as.numeric(begin), 
         end = as.numeric(as.POSIXct("2017-08-17 17:04:36", tz="UTC")))
Time Series:
Start = c(1502989474, 1) 
End = c(1502989476, 1) 
Frequency = 2 
[1] 9.455453 4.596560 9.675503 7.437548 2.722311

How to create a time series object yyyy-mm-dd hh:mm:ss?

1 Answers