R - hist plot colours by quantile

Question

I am trying to do a simple hist plot and colour the bins by quantile .

I was wondering why when the bins size change the colours gets all messed up. Maybe I am not doing it right from the beginning.

The quantiles are

quantile(x)
    0%    25%    50%    75%   100% 
    0.00  33.75  58.00  78.25 123.00 

Then I am setting the colours with the quantile values

k = ifelse(test = x <= 34, yes = "#8DD3C7", 
no = ifelse(test = (x > 34 & x <= 58), yes =  "#FFFFB3", 
no = ifelse(test = (x > 58 & x <= 79), yes = "#BEBADA", 
no = ifelse(test = (x > 79), yes = "#FB8072", 'grey'))) )                      

Then when I plot with larger bin, I get :

hist(dt, breaks = 10, col = k) 

Which seems right, even though the last bin is wrong (?!).

But when I try with smaller bins, the colours are not right.

Could someone help me understand why is it wrong ? Or if my code is wrong ?

The x in question

x = c(23, 23, 16, 16, 34, 34, 43, 43, 97, 97, 63, 63, 39, 39, 29, 
29, 63, 63, 48, 48, 7, 7, 80, 80, 69, 69, 110, 110, 103, 103, 
43, 43, 39, 39, 46, 46, 14, 14, 56, 56, 76, 76, 52, 52, 18, 18, 
32, 32, 66, 66, 70, 70, 26, 26, 40, 40, 105, 105, 62, 62, 51, 
51, 58, 58, 37, 37, 55, 55, 42, 42, 11, 11, 89, 89, 55, 55, 109, 
109, 49, 49, 27, 27, 96, 96, 27, 27, 65, 65, 74, 74, 17, 17, 
33, 33, 89, 89, 63, 63, 18, 18, 25, 25, 36, 36, 108, 108, 3, 
3, 52, 52, 83, 83, 74, 74, 56, 56, 99, 99, 6, 6, 25, 25, 51, 
51, 4, 4, 100, 100, 17, 17, 44, 44, 23, 23, 70, 70, 85, 85, 14, 
14, 22, 22, 89, 89, 45, 45, 2, 2, 29, 29, 14, 14, 69, 69, 96, 
96, 10, 10, 58, 58, 97, 97, 54, 54, 60, 60, 65, 65, 2, 2, 54, 
54, 4, 4, 28, 28, 107, 107, 74, 74, 72, 72, 71, 71, 42, 42, 92, 
92, 64, 64, 39, 39, 111, 111, 72, 72, 73, 73, 58, 58, 41, 41, 
56, 56, 73, 73, 18, 18, 73, 73, 36, 36, 60, 60, 49, 49, 47, 47, 
95, 95, 19, 19, 8, 8, 7, 7, 38, 38, 38, 38, 38, 38, 28, 28, 79, 
79, 53, 53, 30, 30, 19, 19, 14, 14, 53, 53, 68, 68, 39, 39, 42, 
42, 87, 87, 33, 33, 18, 18, 77, 77, 83, 83, 19, 19, 14, 14, 7, 
7, 32, 32, 94, 94, 30, 30, 55, 55, 89, 89, 30, 30, 45, 45, 84, 
84, 38, 38, 59, 59, 73, 73, 77, 77, 22, 22, 55, 55, 31, 31, 52, 
52, 20, 20, 26, 26, 62, 62, 55, 55, 46, 46, 26, 26, 49, 49, 22, 
22, 65, 65, 67, 67, 73, 73, 29, 29, 88, 88, 86, 86, 76, 76, 32, 
32, 12, 12, 19, 19, 14, 14, 8, 8, 63, 63, 63, 63, 65, 65, 84, 
84, 34, 34, 42, 42, 26, 26, 75, 75, 68, 68, 28, 28, 95, 95, 17, 
17, 76, 76, 33, 33, 91, 91, 93, 93, 80, 80, 89, 89, 64, 64, 81, 
81, 98, 98, 47, 47, 70, 70, 46, 46, 11, 11, 92, 92, 69, 69, 95, 
95, 51, 51, 87, 87, 61, 61, 50, 50, 47, 47, 35, 35, 31, 31, 39, 
39, 19, 19, 81, 81, 35, 35, 68, 68, 68, 68, 67, 67, 57, 57, 7, 
7, 9, 9, 23, 23, 50, 50, 89, 89, 41, 41, 54, 54, 53, 53, 57, 
57, 89, 89, 32, 32, 40, 40, 48, 48, 35, 35, 15, 15, 90, 90, 1, 
1, 17, 17, 53, 53, 73, 73, 76, 76, 59, 59, 45, 45, 68, 68, 21, 
21, 37, 37, 33, 33, 51, 51, 61, 61, 31, 31, 15, 15, 23, 23, 29, 
29, 45, 45, 96, 96, 87, 87, 37, 37, 104, 104, 50, 50, 58, 58, 
103, 103, 91, 91, 72, 72, 73, 73, 27, 27, 60, 60, 23, 23, 99, 
99, 28, 28, 78, 78, 27, 27, 82, 82, 63, 63, 34, 34, 84, 84, 62, 
62, 2, 2, 99, 99, 22, 22, 85, 85, 39, 39, 47, 47, 66, 66, 17, 
17, 74, 74, 45, 45, 70, 70, 87, 87, 28, 28, 97, 97, 89, 89, 33, 
33, 50, 50, 79, 79, 86, 86, 69, 69, 91, 91, 75, 75, 52, 52, 76, 
76, 13, 13, 71, 71, 42, 42, 20, 20, 28, 28, 56, 56, 69, 69, 16, 
16, 47, 47, 60, 60, 45, 45, 72, 72, 78, 78, 107, 107, 4, 4, 64, 
64, 88, 88, 9, 9, 3, 3, 10, 10, 92, 92, 41, 41, 5, 5, 35, 35, 
31, 31, 24, 24, 70, 70, 47, 47, 41, 41, 32, 32, 92, 92, 90, 90, 
75, 75, 3, 3, 78, 78, 30, 30, 93, 93, 60, 60, 17, 17, 25, 25, 
48, 48, 70, 70, 69, 69, 66, 66, 76, 76, 104, 104, 31, 31, 72, 
72, 56, 56, 64, 64, 92, 92, 68, 68, 102, 102, 100, 100, 27, 27, 
40, 40, 47, 47, 29, 29, 76, 76, 78, 78, 20, 20, 13, 13, 10, 10, 
113, 113, 17, 17, 61, 61, 69, 69, 65, 65, 16, 16, 100, 100, 5, 
5, 18, 18, 24, 24, 54, 54, 41, 41, 64, 64, 66, 66, 90, 90, 29, 
29, 97, 97, 37, 37, 42, 42, 84, 84, 37, 37, 74, 74, 65, 65, 12, 
12, 49, 49, 31, 31, 108, 108, 9, 9, 93, 93, 71, 71, 39, 39, 70, 
70, 79, 79, 92, 92, 60, 60, 104, 104, 79, 79, 103, 103, 38, 38, 
93, 93, 46, 46, 66, 66, 79, 79, 51, 51, 31, 31, 65, 65, 93, 93, 
25, 25, 22, 22, 91, 91, 123, 123, 51, 51, 34, 34, 64, 64, 31, 
31, 24, 24, 74, 74, 57, 57, 95, 95, 83, 83, 28, 28, 56, 56, 72, 
72, 43, 43, 18, 18, 66, 66, 32, 32, 17, 17, 67, 67, 10, 10, 44, 
44, 66, 66, 57, 57, 89, 89, 57, 57, 55, 55, 18, 18, 78, 78, 82, 
82, 103, 103, 110, 110, 92, 92, 54, 54, 35, 35, 8, 8, 53, 53, 
86, 86, 45, 45, 99, 99, 19, 19, 84, 84, 94, 94, 92, 92, 80, 80, 
69, 69, 45, 45, 22, 22, 59, 59, 9, 9, 41, 41, 72, 72, 24, 24, 
117, 117, 79, 79, 57, 57, 29, 29, 96, 96, 47, 47, 23, 23, 64, 
64, 33, 33, 48, 48, 80, 80, 30, 30, 42, 42, 10, 10, 42, 42, 68, 
68, 46, 46, 58, 58, 39, 39, 82, 82, 79, 79, 80, 80, 89, 89, 85, 
85, 24, 24, 106, 106, 40, 40, 90, 90, 69, 69, 92, 92, 84, 84, 
82, 82, 86, 86, 80, 80, 73, 73, 78, 78, 39, 39, 27, 27, 55, 55, 
100, 100, 63, 63, 21, 21, 46, 46, 94, 94, 6, 6, 45, 45, 66, 66, 
94, 94, 52, 52, 78, 78, 59, 59, 86, 86, 67, 67, 76, 76, 54, 54, 
47, 47, 37, 37, 76, 76, 32, 32, 49, 49, 87, 87, 122, 122, 27, 
27, 82, 82, 51, 51, 50, 50, 22, 22, 32, 32, 99, 99, 77, 77, 54, 
54, 29, 29, 82, 82, 80, 80, 85, 85, 30, 30, 57, 57, 41, 41, 50, 
50, 65, 65, 51, 51, 109, 109, 89, 89, 50, 50, 6, 6, 66, 66, 42, 
42, 48, 48, 88, 88, 67, 67, 89, 89, 109, 109, 80, 80, 64, 64, 
64, 64, 95, 95, 76, 76, 76, 76, 78, 78, 44, 44, 51, 51, 19, 19, 
29, 29, 31, 31, 75, 75, 11, 11, 10, 10, 64, 64, 80, 80, 29, 29, 
73, 73, 67, 67, 38, 38, 27, 27, 23, 23, 74, 74, 79, 79, 49, 49, 
78, 78, 29, 29, 59, 59, 70, 70, 8, 8, 24, 24, 39, 39, 80, 80, 
27, 27, 29, 29, 36, 36, 94, 94, 86, 86, 35, 35, 84, 84, 99, 99, 
83, 83, 92, 92, 81, 81, 58, 58, 2, 2, 64, 64, 75, 75, 29, 29, 
53, 53, 58, 58, 11, 11, 38, 38, 83, 83, 108, 108, 86, 86, 56, 
56, 12, 12, 84, 84, 76, 76, 38, 38, 54, 54, 37, 37, 27, 27, 61, 
61, 83, 83, 37, 37, 59, 59, 81, 81, 76, 76, 70, 70, 61, 61, 101, 
101, 77, 77, 68, 68, 74, 74, 83, 83, 70, 70, 93, 93, 53, 53, 
64, 64, 89, 89, 1, 1, 53, 53, 67, 67, 81, 81, 71, 71, 51, 51, 
85, 85, 35, 35, 67, 67, 53, 53, 37, 37, 31, 31, 65, 65, 82, 82, 
47, 47, 60, 60, 81, 81, 21, 21, 94, 94, 75, 75, 92, 92, 113, 
113, 93, 93, 84, 84, 77, 77, 82, 82, 84, 84, 58, 58, 83, 83, 
84, 84, 80, 80, 1, 1, 49, 49, 73, 73, 22, 22, 99, 99, 74, 74, 
28, 28, 33, 33, 74, 74, 91, 91, 83, 83, 70, 70, 99, 99, 69, 69, 
38, 38, 68, 68, 47, 47, 61, 61, 47, 47, 70, 70, 85, 85, 20, 20, 
100, 100, 3, 3, 49, 49, 100, 100, 85, 85, 54, 54, 8, 8, 3, 3, 
47, 47, 46, 46, 45, 45, 27, 27, 87, 87, 20, 20, 24, 24, 51, 51, 
50, 50, 105, 105, 73, 73, 13, 13, 18, 18, 51, 51, 75, 75, 55, 
55, 62, 62, 85, 85, 56, 56, 51, 51, 66, 66, 74, 74, 63, 63, 2, 
2, 81, 81, 85, 85, 19, 19, 16, 16, 83, 83, 36, 36, 79, 79, 63, 
63, 41, 41, 45, 45, 76, 76, 62, 62, 67, 67, 74, 74, 92, 92, 47, 
47, 41, 41, 80, 80, 57, 57, 100, 100, 66, 66, 58, 58, 65, 65, 
59, 59, 20, 20, 54, 54, 10, 10, 79, 79, 64, 64, 106, 106, 44, 
44, 28, 28, 41, 41, 49, 49, 80, 80, 61, 61, 20, 20, 75, 75, 59, 
59, 93, 93, 32, 32, 38, 38, 30, 30, 41, 41, 8, 8, 8, 8, 54, 54, 
56, 56, 83, 83, 81, 81, 77, 77, 42, 42, 59, 59, 11, 11, 21, 21, 
77, 77, 84, 84, 86, 86, 84, 84, 34, 34, 48, 48, 80, 80, 92, 92, 
18, 18, 66, 66, 40, 40, 45, 45, 60, 60, 80, 80, 2, 2, 5, 5, 84, 
84, 66, 66, 70, 70, 70, 70, 95, 95, 62, 62, 0, 0, 67, 67, 61, 
61, 71, 71, 73, 73, 82, 82, 45, 45, 54, 54, 43, 43)

Answer 1

It is because you mistunderstand the col argument of hist .

The col argument is a vector where col[i] is the colour of the i th bar of the histogram.

Your k vector has one element per element of x , which is many more than the number of bars in the histogram.

In the first case, only the first 13 elements of k are used to colour the bars (in that order), since there are only 13 bars. In the second case, the first n elements of k are used to colour the bars, where n is the number of bars (see how the first 13 bars of the small-bin histogram have the same colour as the first 13 of the first histogram?).

If you want to colour the bars by quantile, you will have to work out how many bars are in each quantile (not how many data points), and create your k like that.

To do this, you need to know the histogram breaks - the breakpoints of your bins. The output of hist returns an object where you can get the breakpoints and so on - see ?hist .

# do the histogram counts to get the break points
#  don't plot yet
h <- hist(x, breaks=20, plot=F) # h$breaks and h$mids

To work out the colour the bar should be, you can use either the starting coordinate of each bar (all but the last element of h$breaks ), the ending coordinate of each bar (all but the first element of h$breaks ) or the midpoint coordinate of each bar ( h$mids ). Set your colours like you did above.

The findInterval(h$mids, quantile(x), ...) works out which quantile each bar is in (determined by the bar's midpoint); it returns an integer with which interval it is in, or 0 if it's outside (though by definition every bar of the histogram is between the 0th and 100th quantile, so technically your "grey" colour is not ever used). rightmost.closed makes sure the 100% quantile value is included in the top-most colour bracket. The cols[findInterval(...)+1] is just a cool/tricksy way to do your ifelse(h$mids <= ..., "$8DD3C7", ifelse(h$mids <= ..., .....)) ; you could do it the ifelse way if you prefer.

cols <- c('grey', "#8DD3C7", "#FFFFB3", "#BEBADA", "#FB8072")  
k <- cols[findInterval(h$mids, quantile(x), rightmost.closed=T, all.inside=F) + 1]
# plot the histogram with the colours
plot(h, col=k)

Have a look at k - it is only as long as the number of bars in the histogram, rather than as long as the number of datapoints in x .