CODEWITHSUNDEEP
stringrconditional-statementscharacteraddition
user1538235
user1538235

Reputation: 23

Add character to subset of strings in dataset

Suppose I have a dataset:

test = data.frame(x=c(1:11), y=as.character(c(1:11)))

where the collumn 'y' is made up of characters/strings. Now, I would like to change the strings containing two characters (i.e. test[10,2] & test[11,2]) so that those strings start with a character "0". The result of this would be "010" & "011", whereas the other strings (with only one character) remain the same. To me, the logical solution would be:

test[nchar(test[,2])==2,2] = paste(c("0", test[nchar(test[,2])==2,2]), collapse="")

Indeed, only test[10,2] & test[11,2] are affected. The odd thing is though, that the result is test[10,2] = "01011", and test[11,2] = "01011". This means that all strings having two characters are pasted together with a preceding "0". This definitely is not what I would like to see.

What should I do to add only one character to a string in a dataset when certain conditions (of length) are met? Your answer would be greatly appreciated.

Upvotes: 2

Views: 2885

Answers (3)

James
James

Reputation: 66834

Perhaps it would be more readable using ifelse:

transform(test,y=ifelse(nchar(y)==2,paste0("0",y),y))
    x   y
1   1   1
2   2   2
3   3   3
4   4   4
5   5   5
6   6   6
7   7   7
8   8   8
9   9   9
10 10 010
11 11 011

Upvotes: 3

Eli Sander
Eli Sander

Reputation: 1248

I would do the same thing as ttmaccer suggests, except that I would use paste0, which automatically concatenates them without any spaces. It's a bit more efficient than paste, so it can be worth doing if you have a large dataset. It means you don't have to remember the 'sep' argument either.

test[nchar(test[,2])==2,2] = paste0("0", test[nchar(test[,2])==2,2])

Upvotes: 2

shhhhimhuntingrabbits
shhhhimhuntingrabbits

Reputation: 7475

use 

paste("0", test[nchar(test[,2])==2,2], sep="")

so for example

> test[nchar(test[,2])==2,2] = paste("0", test[nchar(test[,2])==2,2], sep="")
> test
    x   y
1   1   1
2   2   2
3   3   3
4   4   4
5   5   5
6   6   6
7   7   7
8   8   8
9   9   9
10 10 010
11 11 011

collapse and sep have different properties

> paste(1,c(2:3),collapse=',')
[1] "1 2,1 3"
> paste(1,c(2:3),sep=',')
[1] "1,2" "1,3"

Upvotes: 4

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