Linux Support 802.1Ag and Y1731

Extract previous value by group from other group column

One option is to create a row number column on DF, then use data.table rolling join:

library(data.table)
setDT(DF)[, rn := seq_len(.N)]

DF[DF, 
    on=.(ID_2 = ID_1, rn = rn), 
    .(ID_1 = i.ID_1, ID_2 = i.ID_2, Value = i.Value, New = x.Value), 
    roll=Inf
]

#    ID_1 ID_2 Value New
# 1:    A    G    10  NA
# 2:    B    D     9  NA
# 3:    C    I    15  NA
# 4:    D    A    27   9
# 5:    A    J     3  27
# 6:    A    B    28  27
# 7:    B    K     4  28
# 8:    E    D     3  NA
# 9:    D    A    11   3
#10:    F    H    19  NA
#11:    H    A    12  19

Unable to append group to user gropus with usermod

Your '-' character is incorrect. Maybe you've copy and paste it from somewhere or you're using a non-standard keyboard.
Take a look at your command hex-dump:

echo 'usermod –a –G support user1' | hd
00000000  75 73 65 72 6d 6f 64 20  e2 80 93 61 20 e2 80 93  |usermod ...a ...|
00000010  47 20 73 75 70 70 6f 72  74 20 75 73 65 72 31 0a  |G support user1.|
00000020

But the correct one is:

echo 'usermod -a -G support user1' | hd
00000000  75 73 65 72 6d 6f 64 20  2d 61 20 2d 47 20 73 75  |usermod -a -G su|
00000010  70 70 6f 72 74 20 75 73  65 72 31 0a              |pport user1.|
0000001c

Notice the - character in the second hex and compare it with your

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