data.matrix: Convert a Data Frame to a Numeric Matrix

data.matrixR Documentation

Convert a Data Frame to a Numeric Matrix


Return the matrix obtained by converting all the variables in a data frame to numeric mode and then binding them together as the columns of a matrix. Factors and ordered factors are replaced by their internal codes.


data.matrix(frame, rownames.force = NA)



a data frame whose components are logical vectors, factors or numeric or character vectors.


logical indicating if the resulting matrix should have character (rather than NULL) rownames. The default, NA, uses NULL rownames if the data frame has ‘automatic’ row.names or for a zero-row data frame.


Logical and factor columns are converted to integers. Character columns are first converted to factors and then to integers. Any other column which is not numeric (according to is.numeric) is converted by as.numeric or, for S4 objects, as(, "numeric"). If all columns are integer (after conversion) the result is an integer matrix, otherwise a numeric (double) matrix.


If frame inherits from class "data.frame", an integer or numeric matrix of the same dimensions as frame, with dimnames taken from the row.names (or NULL, depending on rownames.force) and names.

Otherwise, the result of as.matrix.


The default behaviour for data frames differs from R < 2.5.0 which always gave the result character rownames.


Chambers, J. M. (1992) Data for models. Chapter 3 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.

See Also

as.matrix, data.frame, matrix.


DF <- data.frame(a = 1:3, b = letters[10:12],
                 c = seq(as.Date("2004-01-01"), by = "week", length.out = 3),
                 stringsAsFactors = TRUE)