[R] replacing a value

[ani jaya]

Dear R-Help,

I try to change a specific value here by following these:

https://www.journaldev.com/39695/replace-in-r
https://stackoverflow.com/questions/5824173/replace-a-value-in-a-data-frame-based-on-a-conditional-if-statement
https://stackoverflow.com/questions/54615462/how-to-replace-certain-values-in-a-specific-rows-and-columns-with-na-in-r
..and many more

however, it is not change anything. I believe it "should" be easy but
I think I am missing something. I am afraid it is my system that has a
problem but restarting r is not solve the problem.
I just want to change 20 to 0 in my data.

> dput(a)
c(20, 20, 14.2375646029948, 19.9999999999999, 20, 20, 16.3092078677214,
20, 20, 20, 20, 20, 20, 20, 20, 14.8590932408795, 16.178935255298,
20, 20, 20, 20, 27.6404077886079, 20, 20, 20, 20, 20, 21.9857063037444,
20, 20, 20, 20)

what I did:
a[a==20]<-0 #fail
a<-replace(a,a==20,0) #fail
a[which(a==20)]<-0 #fail

> sessionInfo()
R version 4.1.2 (2021-11-01)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 19043)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
system code page: 949

Best,
Ani