如何使用基础 R 中的 for 循环计算唯一值的数量？

Question

I have a big data frame and would like to count the number of unique values per column using a for-loop and base R - so no n_distinct or apply family functions. It has columns that aren't numerical or integer

Answer 1

If we need a for loop - initialize a list to store the output, then loop over the sequence of columns, extract the column ( df1[[i]] ), get the unique values, find the length and store that in the corresponding list element. Note that list is just one way to store the object in case if the object is complex. Otherwise, we can also do out <- integer(ncol(df)) as initialization which returns a integer vector

out <- vector('list', ncol(df1))
for(i in seq_along(df1))
  out[[i]] <- length(unique(df1[[i]]))