[R] Does R have an equivalent for Matlab's cell array?
David Winsemius
dwinsemius at comcast.net
Sat Dec 22 20:28:01 CET 2012
On Dec 22, 2012, at 2:58 AM, Matthijs Daelman wrote:
> Hi
>
> I have a time series of measurements: every 10 min. a value was logged.
>
> The data look like:
>
> 20100914 08:01 3.74
> 20100914 08:11 3.74
> 20100914 08:21 3.71
> 20100914 08:31 4.39
> 20100914 08:41 3.74
>
> This data spans several months.
>
> I would like to group the data per day. In Matlab it is fairly easy to obtain a cell array, of which the first column contains the date of each day, and the second column contains a vector, that in its turn contains all values for the corresponding day.
>
> That looks like
>
> 14-9-2010 [3.74 3.74 3.71 4.39 3.74...]
> 15-9-2010 [...]
> and so on.
>
> Is it possible to create a similar data structure in in R? I was thinking of a data frame, similar to the Matlab's cell array, but it doesn't look like data frames can contain vectors.
That's a surprising conclusion. Vectors are typical components of dataframes.
> Something like a two dimensional list would do the trick, I believe, but does that exist?
A dataframe _is_ a two-dimensional list.
You should probably explain what you are trying to do, since there is very possibly a better way of structuring this problem without recasting the data into a "wide format". Most of the data processing in R is handled very well without such a strategy.
If you wanted to proceed despite my misgivings, then there are several functions such as `split`, `tapply` and `by` that could allow you to segregate such data. It's best to use dput to present the data since console output is often ambiguous as to the underlying data structures.
From what you have offered it's not clear that you have yet done the data input processing.
--
David Winsemius
Alameda, CA, USA
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