Creating new data frame within function

Question

I have a data frame (df) with a column of dates and a column of numbers (either 1, 2 or 3) like so:

Date           Number
01/01/2014     1
01/01/2014     1
01/01/2014     2
01/01/2014     3
02/01/2014     3
02/01/2014     2
02/01/2014     2
02/01/2014     2
03/01/2014     1
03/01/2014     3

I have split this data frame by date using split:

  days <- split(df, df$Date)

I then want to apply a function to each day in the split data frame to count how many times "1", "2" or "3" occurs for each day. This is what I have:

myfunction <- function(df){
One <- length(which(df$Number==1))
Two <- length(which(df$Number==2))
Three <- length(which(df$Number=="NA"))
}

lapply(days, myfunction)

If I use e.g. print(One) at the end of this function it will print the amount of times 1 appears for each day. However, I want to create a new data frame with the date and the number of times each number occurs, which looks like so:

Date          1    2    3

01/01/2014    2    1    1
02/01/2014    0    3    1
03/01/2014    1    0    1

When I try to write this into my function however, I only get one line of the data frame. This is the code I have:

myfunction <- function(df){
One <- length(which(df$Number==1))
Two <- length(which(df$Number==2))
Three <- length(which(df$Number=="NA"))
newdataframe<- data.frame(One=One, Two=Two, Three=Three)
write.csv(newdataframe, file="12345.csv")
}

lapply(days, myfunction)

Here are the errors I am receiving:

Error in file(file, ifelse(append, "a", "w")) : 
cannot open the connection
In addition: Warning message:
In file(file, ifelse(append, "a", "w")) :
cannot open file '12345.csv': Permission denied

I have also tried with append=TRUE.

NB - I haven't got around to adding the dates into my new data frame yet.

dickoa · Accepted Answer · 2014-03-16 11:56:09Z

1

Using xtabs (or table) will make your life easier here.

(mat <- xtabs( ~ Date + Number, data = df))
##             Number
## Date         1 2 3
##   01/01/2014 2 1 1
##   02/01/2014 0 3 1
##   03/01/2014 1 0 1

colnames(mat) <- c("one", "two", "three")
write.csv(mat, file = "12345.csv")

answered Mar 16, 2014 at 11:56

dickoa

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