Al14 - 1 year ago 90

R Question

My data below

`A<-c(1999,1999, 2001, 2001)`

B<-c("A", "D", "A", "D")

df<-data.frame (A, B)

I am applying

`df$C<-apply(df[1], 2, function(x) ifelse(x > 2000, 2000, x))`

to create a new column with values based on a reference column

Output

`A B C`

1 1999 A 1999

2 1999 D 1999

3 2001 A 2000

4 2001 D 2000

Why it does replicate the same colname

`A`

`C`

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Answer Source

We don't need an `apply`

loop for a single column, it can be done with

```
df$C <- ifelse(df[,1] > 2000, 2000, df[,1])
```

In the OP's code, the output is a `matrix`

with a single column and it also have the same column name resulting in a `matrix`

column with dimnames as 'A'

```
str(df)
#'data.frame': 4 obs. of 3 variables:
#$ A: num 1999 1999 2001 2001
#$ B: Factor w/ 2 levels "A","D": 1 2 1 2
#$ C: num [1:4, 1] 1999 1999 2000 2000
# ..- attr(*, "dimnames")=List of 2
# .. ..$ : NULL
# .. ..$ : chr "A"
```

So, the column is already there, but it is a `matrix`

```
df$C
# A
#[1,] 1999
#[2,] 1999
#[3,] 2000
#[4,] 2000
```

Instead of assigning a `matrix`

, it should be converted to a `vector`

```
df$C <- as.vector(apply(df[1], 2, function(x) ifelse(x > 2000, 2000, x)))
df$C
#[1] 1999 1999 2000 2000
```

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