On Oct 29, 2010, at 11:16 PM, Dennis Murphy wrote:
Hi:
x <- matrix(20:35, ncol = 1)
u <- c(1, 4, 5, 6, 11) # 'x values'
m <- c(1, 3, 1, 1, 0.5)
# Function to compute the inner product of the multipliers with the
extracted
# elements of x determined by u
f <- function(mat, inputs, mults) crossprod(mat[inputs], mults)
f(x, u, mults = c(1, 3, 1, 1, 0.5))
[,1]
[1,] 153
20 + 23 * 3 + 24 + 25 + 30 * 0.5
[1] 153
The function is flexible enough to allow you to play with the input
matrix
(although a vector would also work), the 'observation vector' inputs
and the
set of multipliers. Here's one way (not necessarily the most
efficient):
uv <- matrix(sample(1:15, 25, replace = TRUE), ncol = 5)
uv # like an X matrix, where each row provides the input values of
the
vars
[,1] [,2] [,3] [,4] [,5]
[1,] 12 8 11 10 15
[2,] 15 11 14 14 8
[3,] 4 8 4 10 12
[4,] 10 5 2 1 7
[5,] 11 4 9 1 11
# Apply the function f to each row of uv:
apply(uv, 1, function(y) f(x, y, mults = c(1, 3, 1, 1, 0.5)))
[1] 188.0 203.5 171.5 155.0 162.0
The direct matrix version:
crossprod(t(matrix(x[uv], ncol = 5)), c(1, 3, 1, 1, 0.5))
[,1]
[1,] 188.0
[2,] 203.5
[3,] 171.5
[4,] 155.0
[5,] 162.0
Notice that the apply() call returns a vector whereas crossprod()
returns a
matrix.
x[uv] selects the x values associated with the indices in uv and
returns a
vector in column-major order. The crossprod() call transposes the
reshaped
x[uv] and then 'matrix' multiplies it by the vector c(1, 3, 1, 1,
0.5).
HTH,
Dennis
On Fri, Oct 29, 2010 at 3:54 PM, M.Ribeiro
<mresende...@yahoo.com.br> wrote:
So, I am having a tricky reference file to extract information from.
The format of the file is
x 1 + 4 * 3 + 5 + 6 + 11 * 0.5
I saw the beginning of this task as parsing to extract the digits from
a character string (possibly decimal digits in the case of the third
and seventh positions) delimited by <space>+<space> and <space>*<space>:
library(gsubfn)
> x <- "1 + 4 * 3 + 5 + 6 + 11 * 0.5"
xin <- readLines(textConnection(x))
xp <- strapply(xin, "^(\\d+) \\+ (\\d+) \\* (\\d+\\.*\\d*) \\+ (\\d
+) \\+ (\\d+) \\+ (\\d+) \\* (\\d+\\.*\\d*)", c)
sapply(xp, as.numeric)
[,1]
[1,] 1.0
[2,] 4.0
[3,] 3.0
[4,] 5.0
[5,] 6.0
[6,] 11.0
[7,] 0.5
--
David
So, the elements that are not being multiplied (1, 5 and 6) and the
elements
before the multiplication sign (4 and 11) means actually the
reference for
the row in a matrix where I need to extract the element from.
The numbers after the multiplication sign are regular numbers
Ex:
x<-matrix(20:35)
x
[,1]
[1,] 20
[2,] 21
[3,] 22
[4,] 23
[5,] 24
[6,] 25
[7,] 26
[8,] 27
[9,] 28
[10,] 29
[11,] 30
[12,] 31
[13,] 32
[14,] 33
[15,] 34
[16,] 35
I would like to read the rows 1,4,5,6 and 11 and sum then. However
the
numbers in the elements row 4 and 11 are multiplied by 3 and 0.5
So it would be
20 + 23 * 3 + 24 + 25 + 30 * 0.5.
And I have this format in different files so I can't do all by hand.
Can anybody help me with a script that can differentiate this?
Thanks
--
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
