我对一般的编码很陌生，感觉这个问题更多的是结构问题，而不是语法问题。
我有以下数据帧：
mm <- c(0,0,1,30,0,50)
dates <- as.Date(c("2020-06-01", "2020-06-02", "2020-06-03", "2020-06-04", "2020-06-05", "2020-06-06"))
weather <- data.frame(dates, mm)
如果给定日期的降雨量为35毫米或更大，我想创建一个函数和循环来连接字符串和日期。
testfunction <- function() {
if(i >= 35) {
print(paste(c(
"here's the date:",
weather$dates[weather$mm>=35]),
sep = " "))
}}
for (i in weather$mm) {
testfunction()}
现在，如果我在函数之外单独运行日期提取行：
weather$dates[weather$mm>=35]
> "2020-06-06"
但当我在循环中运行它时：
> "here's the date:" "18419"
忽略预期的字符串输出，为什么日期提取不返回与函数外相同的内容？
只是"dates"列的Date类被强制为integer值，而它与character矢量连接(c(
paste(c(
"here's the date:", weather$dates))
#[1] "here's the date:" "18414" "18415" "18416" "18417" "18418" "18419"
我们可以通过使用as.character转换为character来避免这种情况
paste(c(
"here's the date:", as.character(weather$dates)))
功能可以更改为
testfunction <- function() {
if(i >= 35) {
print(paste(c(
"here's the date:",
as.character(weather$dates)[weather$mm>=35]),
sep = " "))
}}
然后应用
for (i in weather$mm) {
testfunction()}
-输出
[1] "here's the date:" "2020-06-06"
此外，还不完全清楚为什么需要连接(如注释中所示(。如果目的是创建一个字符串(目前，它返回多个字符串作为串联的一部分(，我们可以使用paste作为
paste("here's the date: ", weather$dates[weather$mm>=35])
如果我们需要在下一行打印，请使用cat，而paste则使用sep的元素作为n
testfunction <- function() {
if(i >= 35) {
cat(paste(
"here's the date:",
weather$dates[weather$mm>=35],
sep = "n"), "n")
}}
for (i in weather$mm) {
testfunction()}
#here's the date:
#2020-06-06
mm <- c(0,0,1,30,0,50)
dates <- as.character(c("2020-06-01", "2020-06-02", "2020-06-03", "2020-06-04", "2020-06-05", "2020-06-06"))
weather <- data.frame(dates, mm)
testfunction <- function(x) {
if(x >= 35) {
print(paste(c(
"here's the date:",
weather$dates[weather$mm>=35]),
sep = " "))
}}
for (i in weather$mm) {
testfunction(i)
}
#> [1] "here's the date:" "2020-06-06"
创建于2021-06-01由reprex包(v2.0.0(