[R] ZOO: Learning to apply it to my data

Gabor Grothendieck ggrothendieck at gmail.com
Wed Sep 14 02:07:32 CEST 2011

On Tue, Sep 13, 2011 at 7:36 PM, Rich Shepard <rshepard at appl-ecosys.com> wrote:
> On Tue, 13 Sep 2011, Gabor Grothendieck wrote:
>> As in ?zoo a zoo object is a numeric matrix, numeric vector or factor
>> together with an ordered time index which is unique. Its not clear that
>> that is what you have; however, if we can assume that for each value of
>> param we have a unique set of dates then quant could form a multivariate
>> zoo series with Date index.
> Gabor,
>  Perhaps, then, zoo is not the appropriate library for my needs. Let me try
> to clarify; being new to R and certainly new to zoo I may not express myself
> clearly to those of you who are more experienced.
>  On a given date (sampdate) and a given stream (aggregated from multiple
> locations on that stream) a water sample was sent to the laboratory and
> analyzed for a set of chemicals (param). Each param does not have a unique
> set of dates. As my example showed, on 2010-06-30 SO4, Zn, and As
> concentrations were measured on Winters Creek. On 2011-06-06, Cl, SO4, and
> Zn concentrations were measured on the same stream.

In the example data there were no duplicate dates for a given param
value.  If that is not true in general but it is true that there are
no duplicate dates for each stream name/param combination then we
could create a combined split field.  (We also create a data frame DF
first since you have indicated that a data frame is the input.)

Lines <- "stream,sampdate,param,quant
11164 Winters,2010-06-30,SO4,120.000
11165 Winters,2010-06-30,Zn,0.010
11166 Winters,2011-06-06,As,0.005
11167 Winters,2011-06-06,Cl,5.000
11168 Winters,2011-06-06,SO4,150.000
11169 Winters,2011-06-06,Zn,0.010"

DF <- read.csv(textConnection(Lines))

# strip number from stream field creating new split field
# from stream name and param
DF2 <- with(DF, data.frame(
	date.param = paste(sub(".* ", "", stream), param),

z <- read.zoo(DF2, split = 2)

which gives:

> z
           Winters As Winters Cl Winters SO4 Winters Zn
2010-06-30         NA         NA         120       0.01
2011-06-06      0.005          5         150       0.01

Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com

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