I am working on an ARDL model to study the effect of Inflation on Stocks. For that, I wanted to take the first difference of the Inflation variable via interpolation method. Otherwise, after taking the first difference to make the data stationary all lags > 2 will be 0. But I am new to R and can't find any references or articles that could help me with this problem to take the first difference via interpolation technique. I would strongly appreciate all the help or any guidance in this matter.
I am attaching sample data:
structure(list(Date = structure(c(946684800, 949363200, 951868800,
954547200, 957139200, 959817600, 962409600, 965088000, 967766400,
970358400, 973036800, 975628800, 978307200, 980985600, 983404800,
986083200, 988675200, 991353600, 993945600, 996624000, 999302400,
1001894400, 1004572800, 1007164800, 1009843200, 1012521600, 1014940800,
1017619200, 1020211200, 1022889600, 1025481600, 1028160000, 1030838400,
1033430400, 1036108800, 1038700800, 1041379200, 1044057600, 1046476800,
1049155200, 1051747200, 1054425600, 1057017600, 1059696000, 1062374400,
1064966400, 1067644800, 1070236800, 1072915200, 1075593600), tzone = "UTC", class = c("POSIXct",
"POSIXt")), Inflation = c(2.7, 3.2, 3.8, 3.1, 3.2, 3.7, 3.7,
3.4, 3.5, 3.4, 3.4, 3.4, 3.7, 3.5, 2.9, 3.3, 3.6, 3.2, 2.7, 2.7,
2.6, 2.1, 1.9, 1.6, 1.1, 1.1, 1.5, 1.6, 1.2, 1.1, 1.5, 1.8, 1.5,
2, 2.2, 2.4, 2.6, 3, 3, 2.2, 2.1, 2.1, 2.1, 2.2, 2.3, 2, 1.8,
1.9, 1.9, 1.7)), row.names = c(NA, -50L), class = "data.frame")