One error you may encounter in R is:
Error in apply(df$var1, 2, mean) : dim(X) must have a positive length
This error occurs when you attempt to use the apply() function to calculate some metric for a column of a data frame or matrix, yet provide a vector as an argument instead of a data frame or matrix.
This tutorial shares exactly how to fix this error.
How to Reproduce the Error
Suppose we have the following data frame in R:
#create data frame df <- data.frame(points=c(99, 97, 104, 79, 84, 88, 91, 99), rebounds=c(34, 40, 41, 38, 29, 30, 22, 25), blocks=c(12, 8, 8, 7, 8, 11, 6, 7)) #view data frame df points rebounds blocks 1 99 34 12 2 97 40 8 3 104 41 8 4 79 38 7 5 84 29 8 6 88 30 11 7 91 22 6 8 99 25 7
Now suppose we attempt to use the apply() function to calculate the mean value in the ‘points’ column:
#attempt to calculate mean of 'points' column apply(df$points, 2, mean) Error in apply(df$points, 2, mean) : dim(X) must have a positive length
An error occurs because the apply() function must be applied to a data frame or matrix, yet in this example we attempt to apply it to a specific column in the data frame.
How to Fix the Error
The way to fix this error is to simply provide the name of the data frame to the apply() function as follows:
#calculate mean of every column in data frame apply(df, 2, mean) points rebounds blocks 92.625 32.375 8.375
From the output, we can see the mean value of each column in the data frame. For example, the mean value of the ‘points’ column is 92.625.
We can also use this function to only find the mean of specific values in the data frame:
#calculate mean of 'points' and 'blocks' column in data frame apply(df[c('points', 'blocks')], 2, mean) points blocks 92.625 8.375
Lastly, if we’d like to find the mean of just one column then we can use the mean() function without using the apply() function at all:
#calculate mean of 'points' column mean(df$points)  92.625
The following tutorials explain how to troubleshoot other common errors in R:
How to Fix in R: names do not match previous names
How to Fix in R: longer object length is not a multiple of shorter object length
How to Fix in R: contrasts can be applied only to factors with 2 or more levels