I am trying to use the aggregate function to run a function, catsbydat2, that
produces the mean, minimum, maximum, and number of observations of the values
in a dataframe, inJan2Test, by levels of the dataframe variable MyDay. The
output should be in the form of a dataframe.
#my code:
# This function should process a data frame and return a data frame
# containing the mean, minimum, maximum, and number of observations
# in the data frame for each level of MyDay.
catsbyday2 <- function(df){
# Create a matrix to hold the calculated values.
xx <- matrix(nrow=1,ncol=4)
# Give names to the columns.
colnames(xx) <- c("Mean","min","max","Nobs")
cat("This is the matrix that will hold the results\n",xx,"\n")
# For each level of the indexing variable, MyDay, compute the
# mean, minimum, maximum, and number of observations in the
# dataframe passed to the function.
xx[,1] <- mean(df)
xx[,2] <- min(df)
xx[,3] <- max(df)
xx[,4] <- length(df)
cat("These are the dimensions of the matrix in the function",dim(xx),"\n")
print(xx)
return(xx)
}
# Create data frame
inJan2Test <- data.frame(MyDay=rep(c(1,2,3),4),AveragePM2_5=c(10,20,30,
11,21,31,
12,22,32,
15,25,35))
str(inJan2Test)
cat("This is the data frame","\n")
inJan2Test
xx <-
aggregate(inJan2Test[,"AveragePM2_5"],list(inJan2Test[,"MyDay"]),catsbyday2,simplify=FALSE)
xx
class(xx)
str(xx)
names(xx)
# Create a data frame in the format that I expect aggregate would return
examplar <-
data.frame(mean=c(12,22,32),min=c(10,20,30),max=c(15,25,35),length=c(4,4,4))
examplar
str(examplar)
While the output is correct (the mean, mean etc. are correctly calculated), the
format of the output is not what I want.
(1) Although the returned object appears to be a data frame, it does appear to
be a "normal" data frame. (see the output of
(2) The column names I define in the function are not part of the data frame
that is created.
(3) The returned values on each row are separated by commas. I would expect
them to be separated by spaces.
(4) When I run str() on the output it appears that the output dataframe
contains a list.
> str(xx)
'data.frame': 3 obs. of 2 variables:
$ Group.1: num 1 2 3
$ x :List of 3
..$ : num [1, 1:4] 12 10 15 4
.. ..- attr(*, "dimnames")=List of 2
.. .. ..$ : NULL
.. .. ..$ : chr [1:4] "Mean" "min" "max" "Nobs"
..$ : num [1, 1:4] 22 20 25 4
.. ..- attr(*, "dimnames")=List of 2
.. .. ..$ : NULL
.. .. ..$ : chr [1:4] "Mean" "min" "max" "Nobs"
..$ : num [1, 1:4] 32 30 35 4
.. ..- attr(*, "dimnames")=List of 2
.. .. ..$ : NULL
.. .. ..$ : chr [1:4] "Mean" "min" "max" "Nobs"
I want it to simply be a numeric dataframe:
mean min max length
12 10 15 4
22 20 25 4
32 30 35 4
which should return the following str
examplar <-
data.frame(mean=c(12,22,32),min=c(10,20,30),max=c(15,25,35),length=c(4,4,4))
examplar
str(examplar)
'data.frame': 3 obs. of 4 variables:
$ mean : num 12 22 32
$ min : num 10 20 30
$ max : num 15 25 35
$ length: num 4 4 4
John David Sorkin M.D., Ph.D.
Professor of Medicine, University of Maryland School of Medicine;
Associate Director for Biostatistics and Informatics, Baltimore VA Medical
Center Geriatrics Research, Education, and Clinical Center;
PI Biostatistics and Informatics Core, University of Maryland School of
Medicine Claude D. Pepper Older Americans Independence Center;
Senior Statistician University of Maryland Center for Vascular Research;
Division of Gerontology and Paliative Care,
10 North Greene Street
GRECC (BT/18/GR)
Baltimore, MD 21201-1524
Cell phone 443-418-5382
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