宽到长，带有两组变量以重塑

Question

I have a dataset containing 4 dependent variables, 6 independent variables, and 9 covariates. The dataset is arranged in wide format.

I wish to make it in long format, so I can repeat a certain procedure (lm, plot, ...) in a loop, varying the dependent variable and the independent, while keeping the covariates (in lm example).

The data I have looks like:

And I want it like:

If I had only one set of variables (dependent only or independent only), I know how to do it, I would use the reshape function. But how do I do it when I have two sets of variables ? I need to create 24 different combinations of DV and IV while keeping all covariates in every row.

Would appreciate some guidance. Thank you in advance !

Code for generating random data in the shape of my data:

ID = seq(1,5)
DV1 = rnorm(5,0,1)
DV2 = rnorm(5,0,1)
DV3 = rnorm(5,0,1)
DV4 = rnorm(5,0,1)
IV1 = rnorm(5,0,1)
IV2 = rnorm(5,0,1)
IV3 = rnorm(5,0,1)
IV4 = rnorm(5,0,1)
IV5 = rnorm(5,0,1)
IV6 = rnorm(5,0,1)
COV1 = rnorm(5,0,1)
COV2 = rnorm(5,0,1)
COV3 = rnorm(5,0,1)
data = data.frame(ID,DV1,DV2,DV3,DV4,IV1,IV2,IV3,IV4,IV5,IV6,COV1,COV2,COV3)

Answer 1

You can use melt function of reshape2 package with argument id in which you indicate the columns you would like to keep during transformation from wide to narrow format. Please see the code below:

set.seed(123)
ID = seq(1,5)
DV1 = rnorm(5,0,1)
DV2 = rnorm(5,0,1)
DV3 = rnorm(5,0,1)
DV4 = rnorm(5,0,1)
IV1 = rnorm(5,0,1)
IV2 = rnorm(5,0,1)
IV3 = rnorm(5,0,1)
IV4 = rnorm(5,0,1)
IV5 = rnorm(5,0,1)
IV6 = rnorm(5,0,1)
COV1 = rnorm(5,0,1)
COV2 = rnorm(5,0,1)
COV3 = rnorm(5,0,1)
data = data.frame(ID,DV1,DV2,DV3,DV4,IV1,IV2,IV3,IV4,IV5,IV6,COV1,COV2,COV3)

library(reshape2)
data_molten <- melt(data, id = c("ID", "DV1", "DV2", "DV3", "DV4", "COV1", "COV2", "COV3"))
head(data_molten)

Output:

  ID         DV1        DV2        DV3        DV4        COV1       COV2       COV3 variable      value
1  1 -0.56047565  1.7150650  1.2240818  1.7869131  0.25331851  1.5164706  0.3796395      IV1 -1.0678237
2  2 -0.23017749  0.4609162  0.3598138  0.4978505 -0.02854676 -1.5487528 -0.5023235      IV1 -0.2179749
3  3  1.55870831 -1.2650612  0.4007715 -1.9666172 -0.04287046  0.5846137 -0.3332074      IV1 -1.0260044
4  4  0.07050839 -0.6868529  0.1106827  0.7013559  1.36860228  0.1238542 -1.0185754      IV1 -0.7288912
5  5  0.12928774 -0.4456620 -0.5558411 -0.4727914 -0.22577099  0.2159416 -1.0717912      IV1 -0.6250393
6  1 -0.56047565  1.7150650  1.2240818  1.7869131  0.25331851  1.5164706  0.3796395      IV2 -1.6866933