Update

ftplugin/csv.vim

@@ -517,7 +517,13 @@ fu! <sid>WColumn(...) "{{{3
     " Return on which column the cursor is
     let _cur = getpos('.')
     if !exists("b:csv_fixed_width_cols")
-        let line=getline('.')
+        if line('.') > 1 && mode('') != 'n'
+            " in insert mode, get line from above, just in case the current
+            " line is empty
+            let line = getline(line('.')-1)
+        else
+            let line=getline('.')
+        endif
         " move cursor to end of field
         "call search(b:col, 'ec', line('.'))
         call search(b:col, 'ec')
@@ -2398,6 +2404,9 @@ fu! csv#EvalColumn(nr, func, first, last) range "{{{3
     call <sid>CheckHeaderLine()
     let nr = matchstr(a:nr, '^\-\?\d\+')
     let col = (empty(nr) ? <sid>WColumn() : nr)
+    if col == 0
+        let col = 1
+    endif
     " don't take the header line into consideration
     let start = a:first - 1 + s:csv_fold_headerline
     let stop  = a:last  - 1 + s:csv_fold_headerline
@@ -2516,8 +2525,18 @@ fu! CSV_CloseBuffer(buffer) "{{{3
         augroup! CSV_QuitPre
     endtry
 endfu
-        
 
+fu! CSVSum(col, fmt, first, last) "{{{3
+    let first = a:first
+    let last  = a:last
+    if empty(first)
+        let first = 1
+    endif
+    if empty(last)
+        let last = line('$')
+    endif
+    return csv#EvalColumn(a:col, '<sid>SumColumn', first, last)
+endfu
 " Initialize Plugin "{{{2
 let b:csv_start = exists("b:csv_start") ? b:csv_start : 1
 let b:csv_end   = exists("b:csv_end") ? b:csv_end : line('$')