Discussion

Error returned when attempting to calculate mean of data.frame rows

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As of R version 3.0.0 one cannot use functions such as mean(), max(), min(), etc., on data.frame rows. This can be a problem when going through material in the Creating functions lesson, Testing and Documenting section, if one attempts to apply any of these functions to the example dataset rows (e.g., center(dat[4, ], 0). The examples in the lesson are all written to work only with columns, but an error is returned if one tries using rows. This may also be a problem if one attempts to calculate row means or medians in the Analyzing patient data lesson, Manipulating Data section. The recommended solution to this issue is to not apply these functions to data.frame rows. However, one could get around this issue by using the functions rowSums or rowMeans in some cases, or explicitly converting the row to a vector of numeric values (e.g., center(as.numeric(dat[4, ]), 0))