[英]Series of Correlation coefficient calculation
I want to analyse the default data set in R (mtcars data set). 我想分析R中的默认数据集(mtcars数据集)。 I am interested in creating column of correlation coefficients according to the below rule.
我有兴趣根据以下规则创建相关系数列。 Correlation coefficient of only first three observations ((ie, row 1,2,3)) between "mpg" and "wt", then leaving the first row, calculate again correlation coefficient between next three observations (ie, row 2,3,4) between mpg and wt then leaving the first two rows, calculate again correlation coefficient between next three observations (ie, row 3,4,5) between mpg and wt and so on till end.
仅“ mpg”和“ wt”之间的前三个观察值(即第1,2,3行)的相关系数,然后离开第一行,再次计算下三个观察值(即第2,3行, 4)在mpg和wt之间,然后离开前两行,再次计算mpg和wt之间的下三个观测值(即第3、4、5行)之间的相关系数,依此类推直至结束。 For example
例如
cor(mtcars$mpg[c(1,2,3)],mtcars$wt[c(1,2,3)])
cor(mtcars$mpg[c(2,3,4)],mtcars$wt[c(2,3,4)])
cor(mtcars$mpg[c(3,4,5)],mtcars$wt[c(3,4,5)]);
and so on. 等等。 Can anyone help to how to automate this R code using loop etc.
任何人都可以帮助如何使用循环等自动执行此R代码。
Example , see how i need output, i have done it in excel but i need to do it in R. 示例 ,看看我如何需要输出,我已经在excel中完成了,但是我需要在R中完成了。
The value of cor(mtcars$mpg[c(1,2,3)],mtcars$wt[c(1,2,3)])
is -0.8884586; cor(mtcars$mpg[c(1,2,3)],mtcars$wt[c(1,2,3)])
值为-0.8884586; however, the first value in the Correlation column of the output image in the question is not that so there is some error in the image shown relative to the description of what is wanted. 但是,问题中输出图像的“相关性”列中的第一个值不是那个值,因此相对于所需内容的描述,所示图像中存在一些错误。 We will assume that the description is correct and the sample output is not.
我们将假定描述正确,而样本输出不正确。
Try a rolling apply, rollapply
. 尝试滚动应用,
rollapply
。 It applies the function cor2
to a rolling window of width 3. align = "left"
means it uses the current row and the next 2 rows so that the NA values appear at the end as in the image in the question. 它将函数
cor2
应用于宽度为3的滚动窗口cor2
align = "left"
表示它使用当前行和接下来的2行,以便NA值出现在问题图像中的末尾。 fill = NA
causes it to generate NA values for the last 2 elements since there are not 3 more elements for those. fill = NA
导致它为最后2个元素生成NA值,因为没有3个元素。
library(zoo)
mtcars2 <- mtcars[c("mpg", "wt")]
cor2 <- function(x) cor(x[, 1], x[, 2])
transform(mtcars2, cor = rollapply(mtcars2, 3, cor2, by.column = FALSE,
align = "left", fill = NA))
giving: 赠送:
mpg wt cor
Mazda RX4 21.0 2.620 -0.88845855
Mazda RX4 Wag 21.0 2.875 -0.82589964
Datsun 710 22.8 2.320 -0.87097656
Hornet 4 Drive 21.4 3.215 -0.99520846
Hornet Sportabout 18.7 3.440 -0.99985063
Valiant 18.1 3.460 -0.99534538
Duster 360 14.3 3.570 -0.97267882
Merc 240D 24.4 3.190 -0.90784130
Merc 230 22.8 3.150 -0.96247218
Merc 280 19.2 3.440 -0.86602540
Merc 280C 17.8 3.440 -0.99308187
Merc 450SE 16.4 4.070 -0.05428913
Merc 450SL 17.3 3.730 -0.96311366
Merc 450SLC 15.2 3.780 -0.99534934
Cadillac Fleetwood 10.4 5.250 0.05301502
Lincoln Continental 10.4 5.424 -0.98658763
Chrysler Imperial 14.7 5.345 -0.96899291
Fiat 128 32.4 2.200 0.44730718
Honda Civic 30.4 1.615 -0.86317499
Toyota Corolla 33.9 1.835 -0.94182141
Toyota Corona 21.5 2.465 -0.99341821
Dodge Challenger 15.5 3.520 -0.94720046
AMC Javelin 15.2 3.435 0.21168794
Camaro Z28 13.3 3.840 -0.90670560
Pontiac Firebird 19.2 3.845 -0.99864434
Fiat X1-9 27.3 1.935 -0.99939736
Porsche 914-2 26.0 2.140 -0.99630829
Lotus Europa 30.4 1.513 -0.99962223
Ford Pantera L 15.8 3.170 -0.93453339
Ferrari Dino 19.7 2.770 -0.96372018
Maserati Bora 15.0 3.570 NA
Volvo 142E 21.4 2.780 NA
Also see this SO post which is similar except in a data.table context: Rolling correlation with data.table 另请参见此SO帖子,除了在data.table上下文中类似: 与data.table滚动相关
It's not clear to me why you want to calculate what looks to me like a rolling correlation within a 3
row/observation window, but you could do something like this in base R: 对我来说尚不清楚, 为什么要在
3
行/观察窗口内计算看起来像滚动相关性的东西,但是您可以在基本R中执行以下操作:
x <- lapply(seq(1, nrow(mtcars) - 2), function(x) seq(x, x + 2))
Here x
is a list
containing as entries the rows/observations based on which we calculate the correlation. 这里的
x
是一个list
其中包含行/观测值作为条目,我们根据该行/观测值计算相关性。
df <- do.call(rbind, lapply(x, function(x) cor(mtcars$mpg[x], mtcars$wt[x])))
df;
# [,1]
#[1,] -0.88845855
#[2,] -0.82589964
#[3,] -0.87097656
#[4,] -0.99520846
#[5,] -0.99985063
#[6,] -0.99534538
#[7,] -0.97267882
#[8,] -0.90784130
#[9,] -0.96247218
#[10,] -0.86602540
#[11,] -0.99308187
#[12,] -0.05428913
#[13,] -0.96311366
#[14,] -0.99534934
#[15,] 0.05301502
#[16,] -0.98658763
#[17,] -0.96899291
#[18,] 0.44730718
#[19,] -0.86317499
#[20,] -0.94182141
#[21,] -0.99341821
#[22,] -0.94720046
#[23,] 0.21168794
#[24,] -0.90670560
#[25,] -0.99864434
#[26,] -0.99939736
#[27,] -0.99630829
#[28,] -0.99962223
#[29,] -0.93453339
#[30,] -0.96372018
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