如何使用apply，cat和print而不使用NULL [英] How to use apply, cat and print, without getting NULL

问题描述

我正在尝试将cat()用作apply()中的函数.我可以几乎使R做我想做的事，但是在返回的末尾我得到一些(对我来说)非常令人困惑的NULL.这是一个愚蠢的示例，以突出显示我所得到的.

I am trying to use cat() as functions inside apply(). I can almost make R do what I want, but I'm getting some very confusing (to me) NULLS at the end of the return. Here is a silly example, to highlight what I'm getting.

val1 <- 1:10
val2 <- 25:34
values <- data.frame(val1, val2)
apply(values, 1, function(x) cat(x[1], x[2], fill=TRUE))

R中的这个有效"接受并运行，但是我不理解结果.

This "works" in that R accepts it and it runs, but I don't understand the results.

> apply(values, 1, function(x) cat(x[1], x[2], fill=TRUE))
1 25
2 26
3 27
4 28
5 29
6 30
7 31
8 32
9 33
10 34
NULL

但是，我想得到:

> apply(values, 1, function(x) cat(x[1], x[2], fill=TRUE))
1 25
2 26
3 27
4 28
5 29
6 30
7 31
8 32
9 33
10 34

那么，如何删除最终的NULL?

So, how do I remove that final NULL?

推荐答案

NULL是R解释器，它打印您键入的表达式的值-apply.您可以将其分配到某个地方:

The NULL is the R interpreter printing the value of the expression you typed in - the apply. You can either assign it somewhere:

junk = apply(values, 1, function(x) cat(x[1], x[2], fill=TRUE))

在这种情况下，它不会被打印，或将其包裹在不可见"中:

in which case it wont get printed, or wrap it in 'invisible':

invisible(apply(values, 1, function(x) cat(x[1], x[2], fill=TRUE)))

请注意，只有当您以交互方式运行此命令时，才会打印每行，如果它在函数中，您将看不到它.

Note that its only when you run this interactively that each line is printed, if it's in a function you won't see it.

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