Utilizing column names to multiply over all columns

On Aug 16, 2011, at 3:37 PM, Sam Albers wrote:

## Hello there,
## I have an issue where I need to use the value of column names to
multiply with the individual values in a column and I have many
columns to do this over. I have data like this where the column names
are numbers:

mydf <- data.frame(`2.72`=runif(20, 0, 125),
? ? ? ? ? ? ? ? `3.2`=runif(20, 50, 75),
? ? ? ? ? ? ? ? `3.78`=runif(20, 0, 100),
? ? ? ? ? ? ? ? yy= head(letters,2), check.names=FALSE)

mydf

? ? ? ?2.72 ? ? ?3.2 ? ? ?3.78 yy
1 ? 31.07874 74.48555 89.306591 ?a
2 ?123.68290 74.30030 11.943576 ?b
3 ? 89.64024 68.26378 97.627211 ?a
4 ? 81.46604 59.79607 91.005217 ?b

## I had been doing something like this but this seems rather tedious
and clunky. These append the correct values to my dataframe but is
there any way that I can do this generally over each column, also
using each column name as the multiplier for that column?

mydf$vd2.72 <- mydf$'2.72'*2.72
mydf$vd3.2 <- mydf$'3.2'*3.2
mydf$vd3.78 <- mydf$'3.78'*3.78

## So can I get to this point with a more generalized solution? For
now, I would also prefer to keep this in wide format and I am aware
(thanks to the list!) that I could use melt() to get the values I
want.

You will get the warning that last last column is not "going right" but
otherwise this returns what you asked for:

sapply(1:length(mydf), function(i) mydf[[i]]* as.numeric(names(mydf)[i]) ?)
? ? ? ? ? [,1] ? ? [,2] ? ? ?[,3] [,4]
?[1,] ?84.53416 238.3538 337.57891 ? NA
?[2,] 336.41748 237.7610 ?45.14672 ? NA
?[3,] 243.82145 218.4441 369.03086 ? NA
?[4,] 221.58762 191.3474 343.99972 ? NA
?[5,] ?81.78911 213.0770 ?97.90072 ? NA
snipped remainder

--

David Winsemius, MD
West Hartford, CT