R 如果满足条件，如何创建新列？

我想制作一个警告栏，在条件满足时警告数据库用户。我现在有这样的数据

      item       stock_need     rto     doi
PRE 24DX4SX15G    200           4800     14
PLS 12RX10SX15G   240           2400     10
ADU 24PX200ML     700           4800      8
NIS 18PX40SX11G   200           3600      4
REF 500GX12D      200           2400     20

      item       stock_need     rto     doi    rto/doi    warn
PRE 24DX4SX15G    200           4800     14    
PLS 12RX10SX15G   240           2400     10      240    order now
ADU 24PX200ML     700           4800      8      600    order now
NIS 18PX40SX11G   200           3600      4      900
REF 500GX12D      200           2400     20      

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如果doi小于14天，并且rto/doi假设您的数据存储在数据帧df中，我想创建一个新列来警告数据库用户：

warnIdx <- (df$doi < 14) & (df$rto/df$doi <= df$stock_need) # find rows fulfilling both conditions
df$warn <- NA_character_ #add a character column
df$warn[warnIdx] <- "order now" #replace tha NAs with "order now" in said rows

warnIdx