R：如何創建一個基於另一列某些值的新列？

Question

我有一個帶有幾個變量的數據框：

Subj DashedOrQuest ItemNo TimesOrCorrect
1    dashed        243    859
1    dashed        243    648
1    dashed        243    655
1    dashed        243    389
1    question      243    1
1    dashed        244    465
1    dashed        244    844
1    dashed        244    578
1    dashed        244    713
1    question      244    0

我想做的是創建一個新列“ Quest”，以便對於每個ItemNo，都將在TimesOrCorrect中輸入DashedOrQuest中“ question”值的數字。 換句話說，它應該看起來像這樣

Subj DashedOrQuest ItemNo TimesOrCorrect Quest
1    dashed        243    859            1
1    dashed        243    648            1
1    dashed        243    655            1
1    dashed        243    389            1
1    question      243    1              1
1    dashed        244    465            0
1    dashed        244    844            0
1    dashed        244    578            0
1    dashed        244    713            0
1    question      244    0              0

有什么技巧可以在R中做到這一點嗎？ 提前致謝！

Answer 1

library(dplyr)
df%>%group_by(ItemNo)%>%mutate(Quest=TimesOrCorrect[DashedOrQuest=='question'])

Answer 2

我們可以使用data.table

library(data.table)
setDT(df)[, Quest := TimesOrCorrect[DashedOrQuest == "question"], by = .(Subj, ItemNo)]
df
#     Subj DashedOrQuest ItemNo TimesOrCorrect Quest
# 1:    1        dashed    243            859     1
# 2:    1        dashed    243            648     1
# 3:    1        dashed    243            655     1
# 4:    1        dashed    243            389     1
# 5:    1      question    243              1     1
# 6:    1        dashed    244            465     0
# 7:    1        dashed    244            844     0
# 8:    1        dashed    244            578     0
# 9:    1        dashed    244            713     0
#10:    1      question    244              0     0