I have two data frames. One of them contains numbers of questions as text and I use the grep() function to match those numbers to the name of my other dataframe columns.
The problem is that a part of my code doesn't work because my function grep() is not doing the trick.
Basically my two dataframesare as follows
DF1:
| Question | Group |
|---|---|
| 11 | Redmeat |
| 100 | Chicken |
| 56 | Vegetables |
| 210 | Dairy |
DF 2 (values don't matter, only the column name):
| 1.Question | 2.Question | ... | 101.Question | ... | 250.Question |
|---|---|---|---|---|---|
| Yes | No | ... | ... | ... | ... |
| Yes | Yes | ... | ... | ... | ... |
| No | Yes | ... | ... | ... | ... |
| No | Yes | ... | ... | ... | ... |
I use the following code:
i <- n ## I change n according to the row of DF1 that I want
grep(DF1$Question[i], colnames(DF2), fixed = T)
If I do:
i <- 2 ## (Question number 100)
grep(DF1$Question[i], colnames(DF2), fixed = T)
My code returns 100, which is correct since it's the column that corresponds to "100.Question"
But if I do:
i <- 1 ## (Question number 1)
grep(DF1$Question[i], colnames(DF2), fixed = T)
My code returns 1, 11, 21 ... 101 ... 201
Same if i do:
i <- 3 ## (Question number 56)
grep(DF1$Question[i], colnames(DF2), fixed = T)
It returns 56, 156
I only want the exact same number. Even if i use the argument fixed = TRUE it doesn't work.
Is there a solution or an alternative?
CodePudding user response：
Two options: 1) Include the . in the grep pattern, grep(paste0("^", DF1$Question[i], "\\."), colnames(DF2)), or 2) paste the full ".Question" on and use exact matching without any grep at all: paste0(DF1$Question, ".Question"). This will likely be more efficient than regex. Since your code has these is all over the place, I assume you're using a loop. grep and paste are vectorized, so if you provide more context we may be able to help you avoid the loop entirely.
CodePudding user response：
What about specifying in the pattern that you want from the start ^ and you want it to be followed by .Q?
i=3
grep(paste0("^",DF1$Question[i],".Q"), colnames(DF2))
Output:
[1] 56
CodePudding user response：
You need to grep for unique values, therefore you should grep the start of the string ^, together with your number and the dot .. In this case, you cannot use the fixed = T argument, since you are using regex to match.
grep(paste0("^", DF1$Question[i], "\\."), colnames(DF2))