Differenciate numbers from reference for rows

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  
<mresendeufv at 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

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

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?

s <- c("1 + 4 * 3 + 5 + 6 + 11 * 0.5", "1 + 4 * 3 + 5 + 6 + 11 * 0.5")
x <- matrix(20:35)
f <- function(a, b) paste(x[as.numeric(a)], b)
s2 <- gsubfn("([0-9]+)( *\\* *[0-9.]+)?", f, s)
s2

sapply(s2, function(x) eval(parse(text = x)))

On Fri, Oct 29, 2010 at 6:54 PM, M.Ribeiro  
<mresendeufv at 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

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)

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?

I assume that every number except for the second number in the pattern
number * number is to be replaced by that row number in x.  Try this.
We define a regular expression which matches the first number ([0-9]+)
of each potential pair and optionally (?) spaces ( *) a star (\\*),
more spaces ( *) and digits [0-9.]+ passing the first and second
backreferences (matches to the parenthesized portions of the regular
expression) to f and inserting the output of f where the matches had
been.

library(gsubfn)
f <- function(a, b) paste(x[as.numeric(a)], b)
s2 <- gsubfn("([0-9]+)( *\\* *[0-9.]+)?", f, s)

If the objective is to then perform the calculation that that
represents then try this:
sapply(s2, function(x) eval(parse(text = x)))

For example,

s <- c("1 + 4 * 3 + 5 + 6 + 11 * 0.5", "1 + 4 * 3 + 5 + 6 + 11 *  
0.5")
x <- matrix(20:35)
f <- function(a, b) paste(x[as.numeric(a)], b)
s2 <- gsubfn("([0-9]+)( *\\* *[0-9.]+)?", f, s)
s2

[1] "20  + 23  * 3 + 24  + 25  + 30  * 0.5" "20  + 23  * 3 + 24  +  
25 + 30  * 0.5"

sapply(s2, function(x) eval(parse(text = x)))

20  + 23  * 3 + 24  + 25  + 30  * 0.5 20  + 23  * 3 + 24  + 25  +  
30  * 0.5
                                  
153                                   153

For more see the gsubfn home page at http://gsubfn.googlecode.com

On Oct 30, 2010, at 8:42 AM, Gabor Grothendieck wrote:

On Fri, Oct 29, 2010 at 6:54 PM, M.Ribeiro <mresendeufv at 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

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)

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?

I assume that every number except for the second number in the pattern
number * number is to be replaced by that row number in x. ?Try this.
We define a regular expression which matches the first number ([0-9]+)
of each potential pair and optionally (?) spaces ( *) a star (\\*),
more spaces ( *) and digits [0-9.]+ passing the first and second
backreferences (matches to the parenthesized portions of the regular
expression) to f and inserting the output of f where the matches had
been.

library(gsubfn)
f <- function(a, b) paste(x[as.numeric(a)], b)
s2 <- gsubfn("([0-9]+)( *\\* *[0-9.]+)?", f, s)

If the objective is to then perform the calculation that that
represents then try this:
sapply(s2, function(x) eval(parse(text = x)))

For example,

s <- c("1 + 4 * 3 + 5 + 6 + 11 * 0.5", "1 + 4 * 3 + 5 + 6 + 11 * 0.5")
x <- matrix(20:35)
f <- function(a, b) paste(x[as.numeric(a)], b)
s2 <- gsubfn("([0-9]+)( *\\* *[0-9.]+)?", f, s)
s2

[1] "20 ?+ 23 ?* 3 + 24 ?+ 25 ?+ 30 ?* 0.5" "20 ?+ 23 ?* 3 + 24 ?+ 25 + 30
?* 0.5"

sapply(s2, function(x) eval(parse(text = x)))

20 ?+ 23 ?* 3 + 24 ?+ 25 ?+ 30 ?* 0.5 20 ?+ 23 ?* 3 + 24 ?+ 25 ?+ 30 ?*
0.5
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 153 ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 153

For more see the gsubfn home page at http://gsubfn.googlecode.com

I am scratching my head regarding the gsubfn workings. It appears that as
gsubfn moves across the input strings that it will either match just
"[0-9+]" or it will match "[0-9+] *\\* *[0-9.]+?".

In either case the match will do a lookup in x[] for the first match using
the "a" index, and if there is a match for the second position assigned to
"*b" then that x[a] will be followed by "*b" ?and is therefore destined to
be multiplied by "b". I cannot quite figure out how the NULL value gets
not-matched to the second back-reference and then doesn't screw up the f()
function by only providing one argument to a two argument function. Maybe
it's due to this? (So can you comment on how optional back-references return
values?)

s <- "1 + 4 * 3 + 5 + 6 + 11 * 0.5"
g <- function(a, b) sprintf("<a='%s'><b='%s'>", a, b)
gsubfn("([0-9]+)( *\\* *[0-9.]+)?", g, s)