我有太多的变量无法在rowMeans(cbind())函数中手动列出它们。自然地，我试图将它们打包成一个字符矢量，但是它不起作用。我尝试过eval，..，mget，但似乎没人能做到
column_names <- as.vector(summary$variables) #this is where I take the column names from (characters)
dataset[ , means := rowMeans( cbind( eval(column_names) ) , na.rm=TRUE )]
谢谢
答案 0 :(得分：1)
您需要使用.SD和.SDcols来指定相关列；这是一个基于mtcars
library(data.table)
dt <- as.data.table(mtcars)
col_names <- c("mpg", "disp", "drat")
dt[, mean := rowMeans(.SD), .SDcols = col_names]
dt
#mpg cyl disp hp drat wt qsec vs am gear carb mean
#1: 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4 4 61.63333
#2: 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4 4 61.63333
#3: 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 44.88333
#4: 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1 94.16000
#5: 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 127.28333
#6: 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 81.95333
#7: 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4 125.83667
#8: 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 58.26333
#9: 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 55.84000
#10: 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4 63.57333
#11: 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4 63.10667
#12: 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3 98.42333
#13: 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3 98.72333
#14: 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3 98.02333
#15: 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4 161.77667
#16: 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4 157.80000
#17: 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4 152.64333
#18: 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 38.39333
#19: 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 37.01000
#20: 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 36.40667
#21: 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 48.43333
#22: 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2 112.08667
#23: 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2 107.45000
#24: 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4 122.34333
#25: 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2 140.76000
#26: 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 36.79333
#27: 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5 2 50.24333
#28: 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 43.09000
#29: 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5 4 123.67333
#30: 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5 6 56.10667
#31: 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5 8 106.51333
#32: 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2 48.83667
#mpg cyl disp hp drat wt qsec vs am gear carb mean
所以在您的情况下，类似
dataset[ , means := rowMeans(.SD, na.rm = T), .SDcols = column_names]