On Sat, 2007-09-15 at 09:02 -0700, Gerard Smits wrote: > Hi All, > > There are a variety of functions that can be applied to a variable > (column) in a data frame: mean, min, max, sd, range, IQR, etc. > > I am aware of only two that work on the rows, using q1-q3 as example > variables: > > rowMeans(cbind(q1,q2,q3),na.rm=T) #mean of multiple variables > rowSums (cbind(q1,q2,q3),na.rm=T) #sum of multiple variables > > Can the standard column functions (listed in the first sentence) be > applied to rows, with the use of correct indexes to reference the > columns of interest? Or, must these summary functions be programmed > separately to work on a row? > > Thanks, > > Gerard
The answer is: it depends If the row can be coerced to a numeric vector, then yes. This presumes that the data frame contains a single data type or the subset of columns you need contains a single data type. If the row contains multiple data types, then the row becomes a single row data frame or a list and you would have to consider other possible approaches. For example: Taking the first row of the 'iris' dataset becomes a single row data frame: > str(iris[1, ]) 'data.frame': 1 obs. of 5 variables: $ Sepal.Length: num 5.1 $ Sepal.Width : num 3.5 $ Petal.Length: num 1.4 $ Petal.Width : num 0.2 $ Species : Factor w/ 3 levels "setosa","versicolor",..: 1 or if you set 'drop = TRUE', a list: > str(iris[1, , drop = TRUE]) List of 5 $ Sepal.Length: num 5.1 $ Sepal.Width : num 3.5 $ Petal.Length: num 1.4 $ Petal.Width : num 0.2 $ Species : Factor w/ 3 levels "setosa","versicolor",..: 1 If however, you remove the last column Species, which is a factor, you can coerce the remaining object to a numeric matrix: > str(as.matrix(iris[, -5])) num [1:150, 1:4] 5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ... - attr(*, "dimnames")=List of 2 ..$ : NULL ..$ : chr [1:4] "Sepal.Length" "Sepal.Width" "Petal.Length" "Petal.Width" Some functions will do this coercion internally: For example: > rowSums(iris) Error in rowSums(x, prod(dn), p, na.rm) : 'x' must be numeric However: > head(rowSums(iris[, -5])) [1] 10.2 9.5 9.4 9.4 10.2 11.4 HTH, Marc Schwartz ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
