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Array help

8 messages · bfhancock, David Winsemius, Patrick Burns +1 more

Original
bfhancock
# 
Hi! I am learning R and have a question that is probably fairly simple for
those of you much more learned than I.  

I am messing with Arrays and am doing some simple stuff to get the hang of
them.  I will have a seperate array already pulled up and it will have
columns and rows.  I figured out that I can seperate these out with commands
like "array_name"[,1,1].  Now, I have an array where I want to make a single
array from a two ranges in the original array.  from 1:7 and 12:34.  I know
if i just did it with 1:7 it is just "array_name"[1:7,,] and that is it. 
But i wanted 12:34 in there as well. I assumed at first that it would just
be "array_name"[1:7 & 12:34,,] but was wrong.  Can anyone help me with this?
Thanks so much!

-B
Joshua Wiley
# 
Hi B,

What you need to do is pass a vector with the indices you want to
extract.  So, you have 1:7 (which expands to 1, 2, 3, ... 7) and 12:34
(which again expands).  How would you combine two sets of numbers?
c(), the combine or concatenate function.  Putting this in action:

mya <- array(1:510, dim = c(34, 5, 3))

mya[c(1:7, 12:34), , ]

Do note that the row numbers will update unless they were explicitly
named.  So they will be numbered 1:30, not 1:7 and 12:34.

Cheers,

Josh
On Sun, Nov 28, 2010 at 6:36 PM, bfhancock <brianfhancock at gmail.com> wrote:

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      bfhancock
    

    

      
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Josh, the data set is called StatTemps and is in the PASWR package.  I want
to make an array that involves only the 8 a.m. and a separate array that
involves only the 9 a.m. so i can get info on the temperatures in those
groups. So I still want it in the format of StatTemps but in two arrays that
are based on 8 a.m. or 9 a.m.    I have been messing with this for a while.
And no it's not homework, I am just trying to learn R so I am more appealing
out in the field eventually.  They book I am using is confusing!  Hopefully
what I am trying to do isn't confusing.  I want to do an array that holds
the info from 1:6 & 12:22 for 8am and then 7:11 & 23:34 for 9am.  I was able
easily make two arrays based on sex by just putting in StatTemps[1:11,,] &
StatTemps[12:34,,] and assumed I could just go StatTemps[1:6&12:22,,] and
StatTemps[7:11&23:34,,] but that didn't work. Any ideas? Thanks so much!

-B

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      David Winsemius
    

    

      
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On Nov 28, 2010, at 10:56 PM, bfhancock wrote:

        

            

      
      
      
    

        
It may not be an array (since time values don't play very well with  
that data structure.)  If there is time as an index, it may be a more  
complex object such as a time-series or zoo. Check with str().

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Patrick Burns
    

    

      
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Instead of:

   7:11&23:34

I think you mean:

   c(7:11, 23:34)

Using '&' for concatenation
is not an unreasonable idea,
but it is decidedly not what
R does.

It would be instructive to do:

   7:11 & 23:34

at the R prompt to see what you
get.

        
On 29/11/2010 03:56, bfhancock wrote:

            

      
      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        
      

    

    

      
      

        


  

        

      Joshua Wiley
    

    

      
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Hi Brian,

I believe there was some miscommunication earlier due to R's array
class for objects and the colloquial usage of array (the idea that
'array' is used colloquially is a bit odd, but I digress).  In any
case, here are some steps I take (certainly not the only ones) when
exploring a new dataset that I am not familiar with:


## load the package
library(PASWR)

## look at the str()ucture of the object of interest
str(StatTemps)

## Hmm, it is a 'data.frame' with 3 variables
## one variable is 'num' and the other two are 'Factor'
## let's see if we can find out more about those data classes
## (pull up the documentation on each, it can be hard to know at first
##  that 'num' stands for numeric and 'Factor' needs to be lowercase)
?data.frame
?numeric
?factor

## in this case, it is easy to print the whole data set so
StatTemps # print to screen
## but you can also get a nice little summary
summary(StatTemps)

## For the documentation on extraction/indexing
?Extract

## and some examples
StatTemps$temperature
StatTemps$gender
StatTemps$class
## now using a different operator than '$'
## You can call by name by quoting
StatTemps[ , "temperature"]
## or since we know it is column 1
StatTemps[ , 1]
## conversely, we can get row 1
StatTemps[1, ]
## or some combination of rows
StatTemps[c(1:7, 22:34), ]
## or rows and columns
StatTemps[c(1:7, 22:34), c(1, 3)]

## But since you have a factor, there may be an easier way
subset(StatTemps, gender == "Male")
subset(StatTemps, gender == "Female")

subset(StatTemps, class == "8 a.m.")
subset(StatTemps, class == "9 a.m.")

## on more than one variable
subset(StatTemps, class == "8 a.m." & gender == "Male")

## with a continuous variable
subset(StatTemps, temperature < 94)

## and we can do calculations by() groups
by(data = StatTemps$temperature, INDICES = StatTemps$gender, FUN = mean)
## but typing the name is annoying
with(StatTemps, by(data = temperature, INDICES = gender, FUN = mean))
## even more detailed (but leaving off the explicit argument names)
with(StatTemps, by(temperature, list(gender, class), mean))

## A couple visual summaries
boxplot(temperature ~ gender, data = StatTemps)
boxplot(temperature ~ class, data = StatTemps)
## or hop on over to lattice for something a little more advanced
bwplot(temperature ~ gender | class, data = StatTemps)

## and you can select certain parts without subset()
## first let's see what happens with
StatTemps$gender == "Female"
## now if you pass a logical vector to the extraction operator, '['
StatTemps[StatTemps$gender == "Female", ]
## same thing but just the first column
StatTemps[StatTemps$gender == "Female", 1]
## That came out as a vector, but
StatTemps[StatTemps$gender == "Female", 1, drop = FALSE]


HTH,

Josh

        
On Mon, Nov 29, 2010 at 5:01 AM, bfhancock <brianfhancock at gmail.com> wrote: