應用基於列名的函數data.tables [R

Question

我正在尋找應用用戶根據給定的列名定義功能

dt <- data.table(gr_id = 1, id = seq(1,10),min_c = runif(10,10,30), 
       ml_c = runif(10,30,50),mx_c = runif(10,50,100), 
       min_t = runif(10,10,20),ml_t = runif(10,20,25), 
       mx_t = runif(10,25,30)) 

我想適用的計算(min(min)+min(ml))/mx功能對於「c」列和「t」列。目前，我做了如下。然而，當我要添加更多的列變硬（可以說，「一」）

dt[,{ 
    temp1 = min(min_c) 
    temp2 = min(ml_c) 
    temp3 = min(mx_c) 
    score_c = (temp1+temp2)/temp3 
    temp4 = min(min_t) 
    temp5 = min(ml_t) 
    temp6 = min(mx_t) 
    score_t = (temp4+temp5)/temp6 
    list(score_c = score_c, 
     score_t = score_t) 
},by = gr_id 
    ] 

Answer 1

我認爲這會工作。基本思想是使用get。

# the original code could be simplified to: 
dt[, .(
    score_c = (min(min_c) + min(ml_c))/min(mx_c), 
    score_t = (min(min_t) + min(ml_t))/min(mx_t) 
    ), by = gr_id] 
# 
# gr_id score_c score_t 
# 1:  1 0.9051556 1.28054 

# using `get` 
cols <- c('c', 't') 
dt[, { 
    res <- lapply(cols, function(i){ 
     vars <- paste(c('min', 'ml', 'mx'), i, sep = '_') 
     (min(get(vars[1])) + min(get(vars[2])))/min(get(vars[3])) 
    }) 
    names(res) <- paste('score', cols, sep = '_') 
    res 
}, by = gr_id] 

# gr_id score_c score_t 
# 1:  1 0.9051556 1.28054