r 按列其他列分组的列子集的data.table操作

Posted 2021-05-24

# cols_to_scale is a character vector of columns
tmp[, 
      (cols_to_scale) := lapply(.SD, function(col) {
       print(NROW(col))
       scale(col)[,1]
     }), 
     .SDcols = cols_to_scale,
     by = LINE]