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Referencing a column in a function in R

Time:05-01

I am experimenting with writing functions and I was wondering how you apply a function to columns individually. For example, with the mtcars dataset, I would like to compute the z value for each column ( (x - mean(column of x ))/sd(column of x). How do I do that part 'column of x', because I would like to do it for each column individually instead of writing out mtcars$mpg each time for example.

CodePudding user response:

Another option is using the scale function which returns the z score of each column. Here an example using the mtcars dataset:

scale(mtcars)

Output:

                            mpg        cyl        disp          hp        drat           wt        qsec         vs         am       gear       carb
Mazda RX4            0.15088482 -0.1049878 -0.57061982 -0.53509284  0.56751369 -0.610399567 -0.77716515 -0.8680278  1.1899014  0.4235542  0.7352031
Mazda RX4 Wag        0.15088482 -0.1049878 -0.57061982 -0.53509284  0.56751369 -0.349785269 -0.46378082 -0.8680278  1.1899014  0.4235542  0.7352031
Datsun 710           0.44954345 -1.2248578 -0.99018209 -0.78304046  0.47399959 -0.917004624  0.42600682  1.1160357  1.1899014  0.4235542 -1.1221521
Hornet 4 Drive       0.21725341 -0.1049878  0.22009369 -0.53509284 -0.96611753 -0.002299538  0.89048716  1.1160357 -0.8141431 -0.9318192 -1.1221521
Hornet Sportabout   -0.23073453  1.0148821  1.04308123  0.41294217 -0.83519779  0.227654255 -0.46378082 -0.8680278 -0.8141431 -0.9318192 -0.5030337
Valiant             -0.33028740 -0.1049878 -0.04616698 -0.60801861 -1.56460776  0.248094592  1.32698675  1.1160357 -0.8141431 -0.9318192 -1.1221521
Duster 360          -0.96078893  1.0148821  1.04308123  1.43390296 -0.72298087  0.360516446 -1.12412636 -0.8680278 -0.8141431 -0.9318192  0.7352031
Merc 240D            0.71501778 -1.2248578 -0.67793094 -1.23518023  0.17475447 -0.027849959  1.20387148  1.1160357 -0.8141431  0.4235542 -0.5030337
Merc 230             0.44954345 -1.2248578 -0.72553512 -0.75387015  0.60491932 -0.068730634  2.82675459  1.1160357 -0.8141431  0.4235542 -0.5030337
Merc 280            -0.14777380 -0.1049878 -0.50929918 -0.34548584  0.60491932  0.227654255  0.25252621  1.1160357 -0.8141431  0.4235542  0.7352031
Merc 280C           -0.38006384 -0.1049878 -0.50929918 -0.34548584  0.60491932  0.227654255  0.58829513  1.1160357 -0.8141431  0.4235542  0.7352031
Merc 450SE          -0.61235388  1.0148821  0.36371309  0.48586794 -0.98482035  0.871524874 -0.25112717 -0.8680278 -0.8141431 -0.9318192  0.1160847
Merc 450SL          -0.46302456  1.0148821  0.36371309  0.48586794 -0.98482035  0.524039143 -0.13920420 -0.8680278 -0.8141431 -0.9318192  0.1160847
Merc 450SLC         -0.81145962  1.0148821  0.36371309  0.48586794 -0.98482035  0.575139986  0.08464175 -0.8680278 -0.8141431 -0.9318192  0.1160847
Cadillac Fleetwood  -1.60788262  1.0148821  1.94675381  0.85049680 -1.24665983  2.077504765  0.07344945 -0.8680278 -0.8141431 -0.9318192  0.7352031
Lincoln Continental -1.60788262  1.0148821  1.84993175  0.99634834 -1.11574009  2.255335698 -0.01608893 -0.8680278 -0.8141431 -0.9318192  0.7352031
Chrysler Imperial   -0.89442035  1.0148821  1.68856165  1.21512565 -0.68557523  2.174596366 -0.23993487 -0.8680278 -0.8141431 -0.9318192  0.7352031
Fiat 128             2.04238943 -1.2248578 -1.22658929 -1.17683962  0.90416444 -1.039646647  0.90727560  1.1160357  1.1899014  0.4235542 -1.1221521
Honda Civic          1.71054652 -1.2248578 -1.25079481 -1.38103178  2.49390411 -1.637526508  0.37564148  1.1160357  1.1899014  0.4235542 -0.5030337
Toyota Corolla       2.29127162 -1.2248578 -1.28790993 -1.19142477  1.16600392 -1.412682800  1.14790999  1.1160357  1.1899014  0.4235542 -1.1221521
Toyota Corona        0.23384555 -1.2248578 -0.89255318 -0.72469984  0.19345729 -0.768812180  1.20946763  1.1160357 -0.8141431 -0.9318192 -1.1221521
Dodge Challenger    -0.76168319  1.0148821  0.70420401  0.04831332 -1.56460776  0.309415603 -0.54772305 -0.8680278 -0.8141431 -0.9318192 -0.5030337
AMC Javelin         -0.81145962  1.0148821  0.59124494  0.04831332 -0.83519779  0.222544170 -0.30708866 -0.8680278 -0.8141431 -0.9318192 -0.5030337
Camaro Z28          -1.12671039  1.0148821  0.96239618  1.43390296  0.24956575  0.636460997 -1.36476075 -0.8680278 -0.8141431 -0.9318192  0.7352031
Pontiac Firebird    -0.14777380  1.0148821  1.36582144  0.41294217 -0.96611753  0.641571082 -0.44699237 -0.8680278 -0.8141431 -0.9318192 -0.5030337
Fiat X1-9            1.19619000 -1.2248578 -1.22416874 -1.17683962  0.90416444 -1.310481114  0.58829513  1.1160357  1.1899014  0.4235542 -1.1221521
Porsche 914-2        0.98049211 -1.2248578 -0.89093948 -0.81221077  1.55876313 -1.100967659 -0.64285758 -0.8680278  1.1899014  1.7789276 -0.5030337
Lotus Europa         1.71054652 -1.2248578 -1.09426581 -0.49133738  0.32437703 -1.741772228 -0.53093460  1.1160357  1.1899014  1.7789276 -0.5030337
Ford Pantera L      -0.71190675  1.0148821  0.97046468  1.71102089  1.16600392 -0.048290296 -1.87401028 -0.8680278  1.1899014  1.7789276  0.7352031
Ferrari Dino        -0.06481307 -0.1049878 -0.69164740  0.41294217  0.04383473 -0.457097039 -1.31439542 -0.8680278  1.1899014  1.7789276  1.9734398
Maserati Bora       -0.84464392  1.0148821  0.56703942  2.74656682 -0.10578782  0.360516446 -1.81804880 -0.8680278  1.1899014  1.7789276  3.2116766
Volvo 142E           0.21725341 -1.2248578 -0.88529152 -0.54967799  0.96027290 -0.446876870  0.42041067  1.1160357  1.1899014  0.4235542 -0.5030337
attr(,"scaled:center")
       mpg        cyl       disp         hp       drat         wt       qsec         vs         am       gear       carb 
 20.090625   6.187500 230.721875 146.687500   3.596563   3.217250  17.848750   0.437500   0.406250   3.687500   2.812500 
attr(,"scaled:scale")
        mpg         cyl        disp          hp        drat          wt        qsec          vs          am        gear        carb 
  6.0269481   1.7859216 123.9386938  68.5628685   0.5346787   0.9784574   1.7869432   0.5040161   0.4989909   0.7378041   1.6152000 

CodePudding user response:

z_func <- function(x) {((x - mean(x, na.rm = T))/sd(x))}

library(dplyr)
iris %>% 
  mutate(z_sepal = z_func(Sepal.Length))

or if you want to change multiple columns

iris %>% 
  mutate(across(c("Sepal.Length","Petal.Width"), ~z_func(.), .names = "z_{col}"))

CodePudding user response:

Another variation:

library(tidyverse)

get_z <- function(x){
  mtcars |> 
    mutate(z = ({{ x }} - mean({{ x}})) / sd({{ x }}))
}

get_z(mpg)
#>                      mpg cyl  disp  hp drat    wt  qsec vs am gear carb
#> Mazda RX4           21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
#> Mazda RX4 Wag       21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
#> Datsun 710          22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1
#> Hornet 4 Drive      21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
#> Hornet Sportabout   18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
#> Valiant             18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
#> Duster 360          14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
#> Merc 240D           24.4   4 146.7  62 3.69 3.190 20.00  1  0    4    2
#> Merc 230            22.8   4 140.8  95 3.92 3.150 22.90  1  0    4    2
#> Merc 280            19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4
#> Merc 280C           17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
#> Merc 450SE          16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3
#> Merc 450SL          17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3
#> Merc 450SLC         15.2   8 275.8 180 3.07 3.780 18.00  0  0    3    3
#> Cadillac Fleetwood  10.4   8 472.0 205 2.93 5.250 17.98  0  0    3    4
#> Lincoln Continental 10.4   8 460.0 215 3.00 5.424 17.82  0  0    3    4
#> Chrysler Imperial   14.7   8 440.0 230 3.23 5.345 17.42  0  0    3    4
#> Fiat 128            32.4   4  78.7  66 4.08 2.200 19.47  1  1    4    1
#> Honda Civic         30.4   4  75.7  52 4.93 1.615 18.52  1  1    4    2
#> Toyota Corolla      33.9   4  71.1  65 4.22 1.835 19.90  1  1    4    1
#> Toyota Corona       21.5   4 120.1  97 3.70 2.465 20.01  1  0    3    1
#> Dodge Challenger    15.5   8 318.0 150 2.76 3.520 16.87  0  0    3    2
#> AMC Javelin         15.2   8 304.0 150 3.15 3.435 17.30  0  0    3    2
#> Camaro Z28          13.3   8 350.0 245 3.73 3.840 15.41  0  0    3    4
#> Pontiac Firebird    19.2   8 400.0 175 3.08 3.845 17.05  0  0    3    2
#> Fiat X1-9           27.3   4  79.0  66 4.08 1.935 18.90  1  1    4    1
#> Porsche 914-2       26.0   4 120.3  91 4.43 2.140 16.70  0  1    5    2
#> Lotus Europa        30.4   4  95.1 113 3.77 1.513 16.90  1  1    5    2
#> Ford Pantera L      15.8   8 351.0 264 4.22 3.170 14.50  0  1    5    4
#> Ferrari Dino        19.7   6 145.0 175 3.62 2.770 15.50  0  1    5    6
#> Maserati Bora       15.0   8 301.0 335 3.54 3.570 14.60  0  1    5    8
#> Volvo 142E          21.4   4 121.0 109 4.11 2.780 18.60  1  1    4    2
#>                               z
#> Mazda RX4            0.15088482
#> Mazda RX4 Wag        0.15088482
#> Datsun 710           0.44954345
#> Hornet 4 Drive       0.21725341
#> Hornet Sportabout   -0.23073453
#> Valiant             -0.33028740
#> Duster 360          -0.96078893
#> Merc 240D            0.71501778
#> Merc 230             0.44954345
#> Merc 280            -0.14777380
#> Merc 280C           -0.38006384
#> Merc 450SE          -0.61235388
#> Merc 450SL          -0.46302456
#> Merc 450SLC         -0.81145962
#> Cadillac Fleetwood  -1.60788262
#> Lincoln Continental -1.60788262
#> Chrysler Imperial   -0.89442035
#> Fiat 128             2.04238943
#> Honda Civic          1.71054652
#> Toyota Corolla       2.29127162
#> Toyota Corona        0.23384555
#> Dodge Challenger    -0.76168319
#> AMC Javelin         -0.81145962
#> Camaro Z28          -1.12671039
#> Pontiac Firebird    -0.14777380
#> Fiat X1-9            1.19619000
#> Porsche 914-2        0.98049211
#> Lotus Europa         1.71054652
#> Ford Pantera L      -0.71190675
#> Ferrari Dino        -0.06481307
#> Maserati Bora       -0.84464392
#> Volvo 142E           0.21725341

Created on 2022-04-30 by the reprex package (v2.0.1)

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