Thank you for your reply. I didn't state my problem very clearly in my previous
post. The data could look like
a = data.frame(date = c(20081201, 20081202, 20081201), product = c("a b c d e",
"a bdfd c g h t", "def e h a c e h g"), sales = c(1, 2, 3)). The first three
items in "product" are the key, like "a, b c", "a bdfd c" and "def e h" in my
example. It is not necessary just three letters, so substr may not work.
Sorry for the confusion.
HXD
From: Dennis Murphy [mailto:djmu...@gmail.com]
Sent: Wednesday, March 09, 2011 11:30 PM
To: Hui Du
Cc: r-help@r-project.org
Subject: Re: [R] aggregate by part of a field
Hi:
Here's one approach, although I imagine there are more efficient ways.
# A function to strip spaces and return the first three non-blank elements of a
string
keyset <- function(x) substr(gsub(' ', '', x)[1], 1, 3)
# Apply the function to the data frame to generate the key:
a$key <- sapply(a$product, keyset)
> a
date product sales key
1 20081201 a b c d e 1 abc
2 20081202 a b c g h t 2 abc
3 20081201 d e h a c e h g 3 deh
# Use aggregate to sum sales by key:
aggregate(sales ~ key, data = a, FUN = sum)
key sales
1 abc 3
2 deh 3
HTH,
Dennis
On Wed, Mar 9, 2011 at 6:02 PM, Hui Du
<hui...@dataventures.com<mailto:hui...@dataventures.com>> wrote:
Hi All,
I have a data frame like
a = data.frame(date = c(20081201, 20081202, 20081201), product = c("a b c d e",
"a b c g h t", "d e h a c e h g"), sales = c(1, 2, 3))
Now I want to aggregate the sales by part of the a$product.
'Product' is the product name, a string separated by a space. The key in my
aggregate function is first three items in "product" field. In my example, the
key is "a b c", "a b c" and "d e h", respectively. Do you know how to do it? I
thought an awkward way which needed several function calls (like strsplit,
lapply, paste etc) to manipulate the string in 'product' field. I guess there
could be some more elegant way to do it.
Thanks in advance.
HXD
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