我有一些如下所示的数据：
Seller Name Price
ⒽomeⓄnline Harper Hand Truck and Dolly 51.7
HomeOnline Harper Hand Truck and Dolly 62.54
Amazon.com Harper Hand Truck and Dolly 41.83
XpW Honeywell Safe Chest 41.37
XoXoGroupLLC Honeywell Safe Chest 51.78
Toys Online Honeywell Safe Chest 43.01
Tempus & Co. Honeywell Safe Chest 52.7
stores123 Honeywell Safe Chest 51.21
ⒽomeⓄnline Honeywell Safe Chest 43.88
HomeOnline Honeywell Safe Chest 43.87
Great Brands Outlet Honeywell Safe Chest 64.95
Connect Buy Honeywell Safe Chest 30.1
Amazon.com Honeywell Safe Chest 24.6
我想通过Name计算每行与Amazon.com成为卖家的行之间的百分比差异。因此输出看起来像'etc ...'意味着行一直填充：
Seller Name Price Pct_Diff
ⒽomeⓄnline Harper Hand Truck and Dolly 51.7 .23
HomeOnline Harper Hand Truck and Dolly 62.54 .49
Amazon.com Harper Hand Truck and Dolly 41.83
XpW Honeywell Safe Chest 41.37 .68
XoXoGroupLLC Honeywell Safe Chest 51.78 1.0
Toys Online Honeywell Safe Chest 43.01 etc...
Tempus & Co. Honeywell Safe Chest 52.7
stores123 Honeywell Safe Chest 51.21
ⒽomeⓄnline Honeywell Safe Chest 43.88
HomeOnline Honeywell Safe Chest 43.87
Great Brands Outlet Honeywell Safe Chest 64.95
Connect Buy Honeywell Safe Chest 30.1
Amazon.com Honeywell Safe Chest 24.6
我认为这是一个很好的data.table解决方案。但我无法弄清楚如何将没有“Amazon.com”作为卖家的每一行与将“Amazon.com”作为卖家的行进行比较。
答案 0 :(得分：2)
您可以使用：
dt[, pct := (Price - Price[Seller=='Amazon.com'])/Price[Seller=='Amazon.com'], by = Name]
给出：
Seller Name Price pct 1: ⒽomeⓄnline Harper Hand Truck and Dolly 51.70 0.2359551 2: HomeOnline Harper Hand Truck and Dolly 62.54 0.4950992 3: Amazon.com Harper Hand Truck and Dolly 41.83 0.0000000 4: XpW Honeywell Safe Chest 41.37 0.6817073 5: XoXoGroupLLC Honeywell Safe Chest 51.78 1.1048780 6: Toys Online Honeywell Safe Chest 43.01 0.7483740 7: Tempus & Co. Honeywell Safe Chest 52.70 1.1422764 8: stores123 Honeywell Safe Chest 51.21 1.0817073 9: ⒽomeⓄnline Honeywell Safe Chest 43.88 0.7837398 10: HomeOnline Honeywell Safe Chest 43.87 0.7833333 11: Great Brands Outlet Honeywell Safe Chest 64.95 1.6402439 12: Connect Buy Honeywell Safe Chest 30.10 0.2235772 13: Amazon.com Honeywell Safe Chest 24.60 0.0000000
dplyr中实现的逻辑相同：
dt %>%
group_by(Name) %>%
mutate(pct = (Price - Price[Seller=='Amazon.com'])/Price[Seller=='Amazon.com'])
使用过的数据：
dt <- structure(list(Seller = c("ⒽomeⓄnline", "HomeOnline", "Amazon.com", "XpW", "XoXoGroupLLC", "Toys Online", "Tempus & Co.", "stores123", "ⒽomeⓄnline", "HomeOnline", "Great Brands Outlet", "Connect Buy", "Amazon.com"),
Name = c("Harper Hand Truck and Dolly", "Harper Hand Truck and Dolly", "Harper Hand Truck and Dolly", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest"),
Price = c(51.7, 62.54, 41.83, 41.37, 51.78, 43.01, 52.7, 51.21, 43.88, 43.87, 64.95, 30.1, 24.6)),
.Names = c("Seller", "Name", "Price"), class = c("data.table", "data.frame"), row.names = c(NA, -13L))
答案 1 :(得分：1)
这是一个dplyr解决方案
libary(dplyr)
df <- data.frame(
Seller = c("ⒽomeⓄnline", "HomeOnline", "Amazon.com", "XpW", "XoXoGroupLLC", "Toys Online", "Tempus & Co.", "stores123", "ⒽomeⓄnline", "HomeOnline", "Great Brands Outlet", "Connect Buy", "Amazon.com"),
Name = c("Harper Hand Truck and Dolly","Harper Hand Truck and Dolly","Harper Hand Truck and Dolly","Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest", "Honeywell Safe Chest"),
Price = c(51.7, 62.54, 41.83, 41.37, 51.78, 43.01, 52.7, 51.21, 43.88, 43.87, 64.95, 30.1, 24.6)
)
df %>%
# Join each row with the "Amazon.com" price for this item
left_join(df %>% filter(Seller == "Amazon.com"), by = "Name", suffix = c("", ".amazon")) %>%
# Remove unused "Seller" column
select(-Seller.amazon) %>%
# Calculate percentage for each row, except for
# "Amazon.com" rows, for which the percent difference is NA
mutate(Pct_Diff = ifelse(Seller == "Amazon.com", NA, round((Price - Price.amazon) / Price.amazon, 2)))
# Seller Name Price Price.amazon Pct_Diff
# 1 <U+24BD>ome<U+24C4>nline Harper Hand Truck and Dolly 51.70 41.83 0.24
# 2 HomeOnline Harper Hand Truck and Dolly 62.54 41.83 0.50
# 3 Amazon.com Harper Hand Truck and Dolly 41.83 41.83 NA
# 4 XpW Honeywell Safe Chest 41.37 24.60 0.68
# 5 XoXoGroupLLC Honeywell Safe Chest 51.78 24.60 1.10
# 6 Toys Online Honeywell Safe Chest 43.01 24.60 0.75
# 7 Tempus & Co. Honeywell Safe Chest 52.70 24.60 1.14
# 8 stores123 Honeywell Safe Chest 51.21 24.60 1.08
# 9 <U+24BD>ome<U+24C4>nline Honeywell Safe Chest 43.88 24.60 0.78
# 10 HomeOnline Honeywell Safe Chest 43.87 24.60 0.78
# 11 Great Brands Outlet Honeywell Safe Chest 64.95 24.60 1.64
# 12 Connect Buy Honeywell Safe Chest 30.10 24.60 0.22
# 13 Amazon.com Honeywell Safe Chest 24.60 24.60 NA