问题描述
我想更改定义为变量（dataframe）的tibble / col_name列的值。我尝试了!!col_name，但没有成功。
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter,lag
#> The following objects are masked from 'package:base':
#>
#> intersect,setdiff,setequal,union
col_name <- "b" # the column to select
df <- tibble(a = c(1,2,3),b = c(2,4,6))
df %>%
mutate(b = if_else((b == 6 & a == 3),8,b)) # this works
#> # A tibble: 3 x 2
#> a b
#> <dbl> <dbl>
#> 1 1 2
#> 2 2 4
#> 3 3 8
# but this doesn't
df %>%
mutate(!!col_name := if_else((!!col_name == 6 & a == 3),!!col_name))
#> Error: Problem with `mutate()` input `b`.
#> x `false` must be a double vector,not a character vector.
#> i Input `b` is `if_else(("b" == 6 & a == 3),"b")`.
Created on 2020-10-13 by the reprex package (v0.3.0)
解决方法
使用 base ：
df[ df[,col_name ] == 6 & df$a == 3,col_name ] <- 8
df
# a b
# 1 1 2
# 2 2 4
# 3 3 8
注意：是的，我知道这个问题是关于“整洁” 的，这只是为了说明为什么对于一些简单的任务，基本解决方案还是一样好/更好。
,要在RHS上使用#include<iostream>
#include<string>
using namespace std;
int main()
{
//2 rows
int* jagged[2];
//Allocate memeory for the elements in the row 0
jagged[0] = new int[1];
//Allocate memory for the elements in row 1
jagged[1] = new int[5];
//Array to hold the size of each row
int Size[2] = { 1,5 },k = 0,number = 100;
//User enters the numbers
for (int i = 0; i < 2; i++)
{
int* p = jagged[i];
for (int j = 0; j < Size[k]; j++)
{
*p = number++;
//move the pointer
p++;
}
k++;
}
k = 0;
//Display elements in Jagged array
for (int i = 0; i < 2; i++)
{
int* q = jagged[i];
for (int j = 0; j < Size[k]; j++)
{
cout << *q << "";
//move the pointer to the next element
q++;
}
cout << endl;
k++;
//move the pointer to the next row
jagged[i]++;
}
delete[] jagged;
return 0;
}
，您需要先将!!转换为符号。
col_name其他替代方法包括使用library(dplyr)
df %>% mutate(!!col_name := if_else(!!sym(col_name) == 6 & a == 3,8,!!sym(col_name)))
：
get或者没有任何NSE使用df %>% mutate(!!col_name := if_else(get(col_name) == 6 & a == 3,get(col_name)))
：
.data