R help - Jan 2011 - Extraction and replacement of data in a data frame

Dear R family,
I am a relative newbie and have been dabbling with R for a little while. 
Simple things really, but my employers are beginning to see the benefits of
using R instead of excel. We have a remote monitoring station measuring
groundwater levels.  We download the  date as a .csv file and up until now,
we have been using excel to analyse the data.  It?s been a hassle trying to
wrestle with that damn program as my boss wants to do things that excel was
never meant to do,  so I?ve convinced my boss to give R a chance.  It?s been
a steep learning curve, but I?m fairly confident I can reduce the amount of
labour involved in producing and improving the graphs we show our clients.

The groundwater levels are measured by pressure sensors lowered into the
monitoring wells.   After a certain time, the sensors were lowered further
into the well, thus creating a disparity in the measurements.  

The data frame I import into R looks something like this:
Date            Waterhead (mm)
10-01-01     100
10-01-02     105
10-01-03     101
10-01-04      99
10-01-05      85
10-01-06    200
10-01-07    199
10-01-08    195
10-01-09    185
10-01-10    170

For example, on the 10-10-06, the sensor was lowered by 115 mm. 
When I download the csv file, I download the data from the beginning of the
measurement period. I then need to adjust the height by 115 mm to account
for the lowering of the parameter.  My question to you is how do I do that
in R?
I am after a formula or a manipulation that selects the first five
measurements and adds a fixed amount.  This is something that is added
everytime I download the csv file and import it into R so that when I
display my data, it is based on the following data frame:

Date            Waterhead (mm)
10-01-01     215
10-01-02     220
10-01-03     216
10-01-04      214
10-01-05      200
10-01-06    200
10-01-07    199
10-01-08    195
10-01-09    185
10-01-10    170

In short, I want to select a fixed number of rows of a column from my data
frame, add a constant to these, and insert the new values into their
respective rows without affecting the subsequent rows.  I hope I have
produced a reproducible example.  I have been searching high and low for a
solution, but have come up against a brick wall. I feel I have read
something that tackles this some time in the past, but can?t find it again.
Thanks in advance!

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----------------------------------------
> Date: Mon, 17 Jan 2011 12:51:43 -0800
> From: michael.hopgood at mrm.se
> To: r-help at r-project.org
> Subject: [R] Extraction and replacement of data in a data frame
>
>
> Dear R family,
> I am a relative newbie and have been dabbling with R for a little while.
> Simple things really, but my employers are beginning to see the benefits of
> using R instead of excel. We have a remote monitoring station measuring
> groundwater levels. We download the date as a .csv file and up until now,
> we have been using excel to analyse the data. It?s been a hassle trying to
> wrestle with that damn program as my boss wants to do things that excel was
> never meant to do, so I?ve convinced my boss to give R a chance. It?s been
> a steep learning curve, but I?m fairly confident I can reduce the amount of
> labour involved in producing and improving the graphs we show our clients.
>
> The groundwater levels are measured by pressure sensors lowered into the
> monitoring wells. After a certain time, the sensors were lowered further
> into the well, thus creating a disparity in the measurements.
>
> The data frame I import into R looks something like this:
> Date Waterhead (mm)
> 10-01-01 100
> 10-01-02 105
> 10-01-03 101
> 10-01-04 99
> 10-01-05 85
> 10-01-06 200
> 10-01-07 199
> 10-01-08 195
> 10-01-09 185
> 10-01-10 170
>
> For example, on the 10-10-06, the sensor was lowered by 115 mm.
> When I download the csv file, I download the data from the beginning of the
> measurement period. I then need to adjust the height by 115 mm to account
> for the lowering of the parameter. My question to you is how do I do that
> in R?
> I am after a formula or a manipulation that selects the first five
> measurements and adds a fixed amount. This is something that is added
> everytime I download the csv file and import it into R so that when I
> display my data, it is based on the following data frame:

See if this helps, I'm still learning how to do good R but this seems
to work. Just personal pref I converted your data to csv,

?254? cat xxx.txt | awk '{print "20"$1","$2}' >
xxx.csv

I've neer used posix before, just copying what I've seen here but
it seemed to work as shown below, 

x<-read.table("xxx.csv",sep=",")
str(x)
x$V1=as.POSIXct(x$V1)
str(x)
y=(x$V1>as.POSIXct("2010-01-05"))
y
x$V2[y]=x$V2[y]+10000
x


output ends like 

5? 2010-01-05?? 200
6? 2010-01-06 10200
7? 2010-01-07 10199
8? 2010-01-08 10195
9? 2010-01-09 10185
10 2010-01-10 10170


>
> Date Waterhead (mm)
> 10-01-01 215
> 10-01-02 220
> 10-01-03 216
> 10-01-04 214
> 10-01-05 200
> 10-01-06 200
> 10-01-07 199
> 10-01-08 195
> 10-01-09 185
> 10-01-10 170
>
> In short, I want to select a fixed number of rows of a column from my data
> frame, add a constant to these, and insert the new values into their
> respective rows without affecting the subsequent rows. I hope I have
> produced a reproducible example. I have been searching high and low for a
> solution, but have come up against a brick wall. I feel I have read
> something that tackles this some time in the past, but can?t find it again.
> Thanks in advance!
>
> --
> View this message in context:
http://r.789695.n4.nabble.com/Extraction-and-replacement-of-data-in-a-data-frame-tp3221261p3221261.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Hi:

Try this little utility function to see if it meets your needs; the new
variable is for testing; it takes a data frame, adjustment date and
adjustment amount as parameters.

headAdj <- function(df, day, amt) {
   # Check for four or two number year and format accordingly
     u <- unlist(strsplit(day, '-'))[1]
     if(nchar(u) == 4L) day = as.Date(day, format = '%Y-%m-%d') else
         if(nchar(u) == 2L) day = as.Date(day, format = '%y-%m-%d')
   # Make the adjustment and print out the modified data frame
     df$whadj <- df$Waterhead + (df$Date <= day) * amt
     df
   }
> headAdj(df, '2010-01-05', 115)
         Date Waterhead whadj
1  2010-01-01       100   215
2  2010-01-02       105   220
3  2010-01-03       101   216
4  2010-01-04        99   214
5  2010-01-05        85   200
6  2010-01-06       200   200
7  2010-01-07       199   199
8  2010-01-08       195   195
9  2010-01-09       185   185
10 2010-01-10       170   170
> headAdj(df, '10-01-05', 115)
<ditto>

HTH,
Dennis

On Mon, Jan 17, 2011 at 12:51 PM, michael.hopgood
<michael.hopgood@mrm.se>wrote:
>
> Dear R family,
> I am a relative newbie and have been dabbling with R for a little while.
> Simple things really, but my employers are beginning to see the benefits of
> using R instead of excel. We have a remote monitoring station measuring
> groundwater levels.  We download the  date as a .csv file and up until now,
> we have been using excel to analyse the data.  It’s been a hassle trying to
> wrestle with that damn program as my boss wants to do things that excel was
> never meant to do,  so I’ve convinced my boss to give R a chance.  It’s
> been
> a steep learning curve, but I’m fairly confident I can reduce the amount of
> labour involved in producing and improving the graphs we show our clients.
>
> The groundwater levels are measured by pressure sensors lowered into the
> monitoring wells.   After a certain time, the sensors were lowered further
> into the well, thus creating a disparity in the measurements.
>
> The data frame I import into R looks something like this:
> Date            Waterhead (mm)
> 10-01-01     100
> 10-01-02     105
> 10-01-03     101
> 10-01-04      99
> 10-01-05      85
> 10-01-06    200
> 10-01-07    199
> 10-01-08    195
> 10-01-09    185
> 10-01-10    170
>
> For example, on the 10-10-06, the sensor was lowered by 115 mm.
> When I download the csv file, I download the data from the beginning of the
> measurement period. I then need to adjust the height by 115 mm to account
> for the lowering of the parameter.  My question to you is how do I do that
> in R?
> I am after a formula or a manipulation that selects the first five
> measurements and adds a fixed amount.  This is something that is added
> everytime I download the csv file and import it into R so that when I
> display my data, it is based on the following data frame:
>
> Date            Waterhead (mm)
> 10-01-01     215
> 10-01-02     220
> 10-01-03     216
> 10-01-04      214
> 10-01-05      200
> 10-01-06    200
> 10-01-07    199
> 10-01-08    195
> 10-01-09    185
> 10-01-10    170
>
> In short, I want to select a fixed number of rows of a column from my data
> frame, add a constant to these, and insert the new values into their
> respective rows without affecting the subsequent rows.  I hope I have
> produced a reproducible example.  I have been searching high and low for a
> solution, but have come up against a brick wall. I feel I have read
> something that tackles this some time in the past, but can’t find it again.
> Thanks in advance!
>
> --
> View this message in context:
>
http://r.789695.n4.nabble.com/Extraction-and-replacement-of-data-in-a-data-frame-tp3221261p3221261.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

On Mon, Jan 17, 2011 at 3:51 PM, michael.hopgood <michael.hopgood at
mrm.se> wrote:
>
> Dear R family,
> I am a relative newbie and have been dabbling with R for a little while.
> Simple things really, but my employers are beginning to see the benefits of
> using R instead of excel. We have a remote monitoring station measuring
> groundwater levels. ?We download the ?date as a .csv file and up until now,
> we have been using excel to analyse the data. ?It?s been a hassle trying to
> wrestle with that damn program as my boss wants to do things that excel was
> never meant to do, ?so I?ve convinced my boss to give R a chance. ?It?s
been
> a steep learning curve, but I?m fairly confident I can reduce the amount of
> labour involved in producing and improving the graphs we show our clients.
>
> The groundwater levels are measured by pressure sensors lowered into the
> monitoring wells. ? After a certain time, the sensors were lowered further
> into the well, thus creating a disparity in the measurements.
>
> The data frame I import into R looks something like this:
> Date ? ? ? ? ? ?Waterhead (mm)
> 10-01-01 ? ? 100
> 10-01-02 ? ? 105
> 10-01-03 ? ? 101
> 10-01-04 ? ? ?99
> 10-01-05 ? ? ?85
> 10-01-06 ? ?200
> 10-01-07 ? ?199
> 10-01-08 ? ?195
> 10-01-09 ? ?185
> 10-01-10 ? ?170
>
> For example, on the 10-10-06, the sensor was lowered by 115 mm.
> When I download the csv file, I download the data from the beginning of the
> measurement period. I then need to adjust the height by 115 mm to account
> for the lowering of the parameter. ?My question to you is how do I do that
> in R?
> I am after a formula or a manipulation that selects the first five
> measurements and adds a fixed amount. ?This is something that is added
> everytime I download the csv file and import it into R so that when I
> display my data, it is based on the following data frame:
>
> Date ? ? ? ? ? ?Waterhead (mm)
> 10-01-01 ? ? 215
> 10-01-02 ? ? 220
> 10-01-03 ? ? 216
> 10-01-04 ? ? ?214
> 10-01-05 ? ? ?200
> 10-01-06 ? ?200
> 10-01-07 ? ?199
> 10-01-08 ? ?195
> 10-01-09 ? ?185
> 10-01-10 ? ?170
>
> In short, I want to select a fixed number of rows of a column from my data
> frame, add a constant to these, and insert the new values into their
> respective rows without affecting the subsequent rows. ?I hope I have
> produced a reproducible example. ?I have been searching high and low for a
> solution, but have come up against a brick wall. I feel I have read
> something that tackles this some time in the past, but can?t find it again.
> Thanks in advance!
Try this using the builtin data frame, BOD:
> BOD
  Time demand
1    1    8.3
2    2   10.3
3    3   19.0
4    4   16.0
5    5   15.6
6    7   19.8
>
> # add 100 to the first two rows in column 2
> BOD[1:2, 2] <- BOD[1:2, 2] + 100
> BOD
  Time demand
1    1  108.3
2    2  110.3
3    3   19.0
4    4   16.0
5    5   15.6
6    7   19.8



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

Dear all,

Thank you for the prompt responses.  It is until today that I have managed
to scrap together the time to develop my R-project further.  In my free
time, I have been reading various intro manuals, so I have a rough idea of
what needs doing.  Sometimes, though, putting it into practice is more
troublesome than it looks. It is fascinating how pliable this programming
language is.  I will report on my progress as soon as I can.

Sincerely,
Michael Hopgood.
-- 
View this message in context:
http://r.789695.n4.nabble.com/Extraction-and-replacement-of-data-in-a-data-frame-tp3221261p3229476.html
Sent from the R help mailing list archive at Nabble.com.