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I would like to add new columns to an existing data frame. The column names are generated in a FOR loop so that they are numerically sequential. Here is the code:

NewColumn <- paste("return_date", as.character(i), sep = "_")

When I display NewColumn, this is what I want:

[1] "return_date_2"

When I execute:

mutate(Cima, NewColumn = "01-01-01")

The name of the column is: NewColumn

I can rename it, but is there a way to avoid this step? Why does R not recognize that NewColumn holds a string?

thatguy
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XMarlinX
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2 Answers2

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Do you have to use mutate in your code?
If not, replace mutate(Cima, NewColumn = "01-01-01") with Cima[NewColumn] <- "01-01-01"

Nicko
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Because mutate consider the left part of the equal sign to be already the column name. U can get over it with the code below:

library(dplyr)
library(rlang)

i <- 1
NewColumn <- paste("return_date", as.character(i), sep = "_")

> mutate(mtcars, !!NewColumn := 5)

    mpg cyl  disp  hp drat    wt  qsec vs am gear carb return_date_1
1  21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4             5
2  21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4             5
3  22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1             5
4  21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1             5
5  18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2             5
6  18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1             5
7  14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4             5
8  24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2             5
9  22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2             5
10 19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4             5
11 17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4             5
12 16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3             5
13 17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3             5
14 15.2   8 275.8 180 3.07 3.780 18.00  0  0    3    3             5
15 10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4             5
16 10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4             5
17 14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4             5
18 32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1             5
19 30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2             5
20 33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1             5
21 21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1             5
22 15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2             5
23 15.2   8 304.0 150 3.15 3.435 17.30  0  0    3    2             5
24 13.3   8 350.0 245 3.73 3.840 15.41  0  0    3    4             5
25 19.2   8 400.0 175 3.08 3.845 17.05  0  0    3    2             5
26 27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1             5
27 26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2             5
28 30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2             5
29 15.8   8 351.0 264 4.22 3.170 14.50  0  1    5    4             5
30 19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6             5
31 15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8             5
32 21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2             5

Take a look into this one to understand it better:

Use dynamic variable names in `dplyr`

You can also check advanced R from Hadley Wickham and take a look at the bang bang operator and see what it does.

https://adv-r.hadley.nz/

daniellga
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  • Thank you. One unexpected result, though. Using the code above on a column in chr, the column is populated with:c(" ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ", " ... Not what I expected but not disabling. – XMarlinX Aug 16 '20 at 14:02
  • @XMarlinX could you share what you are trying to do? When I replace 5 by 'ok', for example, it still works... – daniellga Aug 16 '20 at 14:14