# Creating an index score (0-11) where 0 = 50% and 11 = highest number. How do I do it quickly and efficiently in R?

Hi there,

I need some help approaching a problem. So, I am a going to create an index score for 14 different variables where the variables are the percentages of observed phenomena across all the census tracts in California.

The index score will go from 0 to 11. 0 = the median (or below) and 11 = the highest recorded observation. I want to be able to calculate a certain census tract index score by converting the percentage to the index score based on where it falls in this spectrum.

I hope that's clear enough. If anyone has any suggestions in terms of best approaches I am open.

Cheers!

Here's an example using the built-in `mtcars` data frame. We use the `rescale` function from the `scales` package

``````library(tidyverse)
library(scales)

mtcars %>%
mutate_all(list(~ifelse(. < median(.), 0, rescale(., to=c(0, 11), from=c(median(.), max(.))))))
``````
Output
``````          mpg cyl      disp        hp        drat         wt       qsec vs am gear      carb
1   1.3469388   0  0.000000  0.000000  1.82591093  0.0000000  0.0000000  0 11    0  3.666667
2   1.3469388   0  0.000000  0.000000  1.82591093  0.0000000  0.0000000  0 11    0  3.666667
3   2.6938776   0  0.000000  0.000000  1.38056680  0.0000000  1.9075145 11 11    0  0.000000
4   1.6462585   0  2.461734  0.000000  0.00000000  0.0000000  3.6666667 11  0    0  0.000000
5   0.0000000  11  6.531375  2.698113  0.00000000  0.6026679  0.0000000  0  0    0  0.000000
6   0.0000000   0  1.145085  0.000000  0.00000000  0.7074798  5.3198459 11  0    0  0.000000
7   0.0000000  11  6.531375  6.330189  0.00000000  1.2839447  0.0000000  0  0    0  3.666667
8   3.8911565   0  0.000000  0.000000  0.00000000  0.0000000  4.8535645 11  0    0  0.000000
9   2.6938776   0  0.000000  0.000000  2.00404858  0.0000000 11.0000000 11  0    0  0.000000
10  0.0000000   0  0.000000  0.000000  2.00404858  0.6026679  1.2504817 11  0    0  3.666667
11  0.0000000   0  0.000000  0.000000  2.00404858  0.6026679  2.5221580 11  0    0  3.666667
12  0.0000000  11  3.171926  2.957547  0.00000000  3.9042401  0.0000000  0  0    0  1.833333
13  0.0000000  11  3.171926  2.957547  0.00000000  2.1224393  0.0000000  0  0    0  1.833333
14  0.0000000  11  3.171926  2.957547  0.00000000  2.3844688  0.6146435  0  0    0  1.833333
15  0.0000000  11 11.000000  4.254717  0.00000000 10.0881372  0.5722543  0  0    0  3.666667
16  0.0000000  11 10.521219  4.773585  0.00000000 11.0000000  0.2331407  0  0    0  3.666667
17  0.0000000  11  9.723250  5.551887  0.00000000 10.5859933  0.0000000  0  0    0  3.666667
18  9.8775510   0  0.000000  0.000000  3.42914980  0.0000000  3.7302505 11 11    0  0.000000
19  8.3809524   0  0.000000  0.000000 11.00000000  0.0000000  1.7167630 11 11    0  0.000000
20 11.0000000   0  0.000000  0.000000  4.67611336  0.0000000  4.6416185 11 11    0  0.000000
21  1.7210884   0  0.000000  0.000000  0.04453441  0.0000000  4.8747592 11  0    0  0.000000
22  0.0000000  11  4.855640  1.400943  0.00000000  1.0219152  0.0000000  0  0    0  0.000000
23  0.0000000  11  4.297062  1.400943  0.00000000  0.5764650  0.0000000  0  0    0  0.000000
24  0.0000000  11  6.132390  6.330189  0.31174089  2.6989042  0.0000000  0  0    0  3.666667
25  0.0000000  11  8.127312  2.698113  0.00000000  2.7251072  0.0000000  0  0    0  0.000000
26  6.0612245   0  0.000000  0.000000  3.42914980  0.0000000  2.5221580 11 11    0  0.000000
27  5.0884354   0  0.000000  0.000000  6.54655870  0.0000000  0.0000000  0 11   11  0.000000
28  8.3809524   0  0.000000  0.000000  0.66801619  0.0000000  0.0000000 11 11   11  0.000000
29  0.0000000  11  6.172289  7.316038  4.67611336  0.0000000  0.0000000  0 11   11  3.666667
30  0.3741497   0  0.000000  2.698113  0.00000000  0.0000000  0.0000000  0 11   11  7.333333
31  0.0000000  11  4.177367 11.000000  0.00000000  1.2839447  0.0000000  0 11   11 11.000000
32  1.6462585   0  0.000000  0.000000  3.69635628  0.0000000  1.8863198 11 11    0  0.000000
``````

For a single vector of values, this would be:

``````# Fake data
set.seed(2)
x = runif(20, 0, 1)

xscaled = ifelse(x < median(x), 0, rescale(x, c(0, 11), from=c(median(x), max(x))))
``````

You can look at what `rescale` is doing by typing `getAnywhere(rescale.numeric)` or `scales:::rescale.numeric` in the console, which gives:

``````function (x, to = c(0, 1), from = range(x, na.rm = TRUE, finite = TRUE), ...) {
if (zero_range(from) || zero_range(to)) {
return(ifelse(is.na(x), NA, mean(to)))
}
(x - from[1])/diff(from) * diff(to) + to[1]
}
``````

To implement this directly:

``````from = c(median(x), max(x))
to = c(0, 11)

xscaled2 = ifelse(x < median(x), 0, (x - from[1])/(from[2] - from[1]) * (to[2] - to[1]) + to[1])
``````

`from[2] - from[1]` is the same as `diff(from)`, but I've used the longer version to make everything explicit.

Thank you for your response @joels

So does this work to create an index score between 0-11 or does it assign 0 or 11 as a binary score?

I think you will be able to answer that question if you run the code in my answer and inspect the output. You can also see the output of the first bit of code by clicking the arrow symbol next to the word "Output" (\blacktriangleright Output) .

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