r - 如何将相同的命令应用于变量列表

Question

我想对一堆变量应用 t 检验。下面是一些模拟数据

d <- data.frame(var1=rnorm(10), 
                var2=rnorm(10), 
                group=sample(c(0,1), 10, replace=TRUE))

# Is there a way to do this in some sort of loop?
with(d, t.test(var1~group))
with(d, t.test(var2~group))

# I tried this but the loop did not give a result!?
varnames <- c('var1', 'var2')
for (i in 1:2) {
  eval(substitute(with(d, t.test(variable~group)),
                  list(variable=as.name(varnames[i]))))  
}

此外，是否可以从 t 检验的结果(例如两组均值、p 值)中提取值，以便循环生成跨变量的简洁平衡表？换句话说，我想要的最终结果不是一堆相互的 t 检验，而是这样的表格:

Varname   mean1   mean2   p-value
Var1        1.1    1.2     0.989
Var2        1.2    1.3     0.912

Answer 1

您可以使用 formula和 lapply像这样

set.seed(1)
d <- data.frame(var1 = rnorm(10), 
                var2 = rnorm(10), 
                group = sample(c(0, 1), 10, replace = TRUE))


varnames <- c("var1", "var2")
formulas <- paste(varnames, "group", sep = " ~ ")
res <- lapply(formulas, function(f) t.test(as.formula(f), data = d))
names(res) <- varnames

如果你想提取你的表，你可以这样进行

t(sapply(res, function(x) c(x$estimate, pval = x$p.value)))
     mean in group 0 mean in group 1     pval
var1         0.61288        0.012034 0.098055
var2         0.46382        0.195100 0.702365