[R] Fwd: converting character matrix to POSIXct matrix

[David Winsemius]

On Apr 26, 2013, at 3:12 PM, hh wt wrote:

> I thought i copy the list for the few suggestions i received privately.
> 
> Thanks to David Winsemius for pointing out that elements of a matrix must
> be atomic. POSIX objects are list, so won't work.

I did state the first point. I didn't actually say that POSIX objects are lists. In fact there are not any "POSIX objects" in R, at least with that exact class name. There is a superclacss of "POSIXt" which some function recognize and perform useful operations on eihter POSIXct and POSIXlt classes . The  POSIXlt-class  is stored as a list. POSIXct vectors, on the other hand, are of mode "numeric" and have a variety of class-specific functions that support math and comparison operations. I did note that matrices cannot hold vectors with classes that make them non-atomic. Perhaps paradoxically, matrices can hold list items.

-- 
David.


> 
> But data frame is an option, as suggested by arun below.
> 
> res<-data.frame(lapply(seq_len(ncol(time.m)),function(i)
> strptime(time.m[,i],"%H:%M:%OS")))
> 
> Thanks to all.
> 
> Horace
> 
> 
> ---------- Forwarded message ----------
> From: arun <smartpink111 at yahoo.com>
> Date: Fri, Apr 26, 2013 at 11:22 AM
> Subject: Re: [R] converting character matrix to POSIXct matrix
> To: hh wt <horacetso at gmail.com>
> Cc: R help <r-help at r-project.org>
> 
> 
> 
> 
> time.m<- as.matrix(read.table(text='
> "08:00:20.799" "08:00:20.799" "08:00:20.799" "08:00:20.799" "08:00:20.799"
> "08:00:21.996" "08:00:22.071" "08:00:23.821" "08:00:24.370" "08:00:25.573"
> "08:00:29.200" "08:00:29.200" "08:00:29.591" "08:00:30.368" "08:00:30.536"
> "08:00:31.073" "08:00:31.372" "08:00:31.384" "08:00:31.403" "08:00:31.867"
> "08:00:31.867" "08:00:31.867" "08:00:31.971" "08:00:34.571" "08:00:34.571"
> ',sep="",header=FALSE,stringsAsFactors=FALSE))
> colnames(time.m)<- NULL
> op<- options(digits.secs=3)
> res<-data.frame(lapply(seq_len(ncol(time.m)),function(i)
> strptime(time.m[,i],"%H:%M:%OS")))
> colnames(res)<- paste0("X",1:5)
>  str(res)
> #'data.frame':    5 obs. of  5 variables:
> # $ X1: POSIXct, format: "2013-04-26 08:00:20.799" "2013-04-26
> 08:00:21.996" ...
> # $ X2: POSIXct, format: "2013-04-26 08:00:20.799" "2013-04-26
> 08:00:22.071" ...
> # $ X3: POSIXct, format: "2013-04-26 08:00:20.799" "2013-04-26
> 08:00:23.821" ...
> # $ X4: POSIXct, format: "2013-04-26 08:00:20.799" "2013-04-26
> 08:00:24.369" ...
> # $ X5: POSIXct, format: "2013-04-26 08:00:20.799" "2013-04-26
> 08:00:25.572" ...
> options(op)
> 
> A.K.
> 
> ----- Original Message -----
> From: hh wt <horacetso at gmail.com>
> To: r-help at r-project.org
> Cc:
> Sent: Friday, April 26, 2013 1:51 PM
> Subject: [R] converting character matrix to POSIXct matrix
> 
> I thought this is a common question but rseek/google searches don't yield
> any relevant hit.
> 
> I have a matrix of character strings, which are time stamps,
> 
>> time.m[1:5,1:5]
>     [,1]           [,2]           [,3]           [,4]           [,5]
> 
> [1,] "08:00:20.799" "08:00:20.799" "08:00:20.799" "08:00:20.799"
> "08:00:20.799"
> [2,] "08:00:21.996" "08:00:22.071" "08:00:23.821" "08:00:24.370"
> "08:00:25.573"
> [3,] "08:00:29.200" "08:00:29.200" "08:00:29.591" "08:00:30.368"
> "08:00:30.536"
> [4,] "08:00:31.073" "08:00:31.372" "08:00:31.384" "08:00:31.403"
> "08:00:31.867"
> [5,] "08:00:31.867" "08:00:31.867" "08:00:31.971" "08:00:34.571"
> "08:00:34.571"
> 
> And i would like to convert it to a POSIXct matrix. I tried this,
> 
> time1 = lapply(time.m, function(tt)strptime(tt, "%H:%M:%OS"))
> 
> but it yields a list.
> 
> Any tip is appreciated.
> 
> 
> Horace
> 
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> 
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> 
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius
Alameda, CA, USA