Encode error

[Linh mt]

Hi everyone,
I have problem with Encode command. My dataset includes 2 variables in string type (reachange2 and reachange3). These vars comprise numeric and text. However, when I use encode command, the numeric data of 'reachange3' var turns to a different number. I also post the example in the .doc file: The numeric '4' of 'reachange3' turns to number '3' of 'lydochange3' after using Encode. (After using encode, 2 new vars are generated respectively 'lydochange2 and lydochange3'.
command: encode reachange3, gen(lydochange3)

province	distric	commune	hoso	reachange2	reachange3	lydochange2	lydochange3
38	388	15046	107
38	388	15046	107
38	388	15046	107	4	4	4	4
38	388	15046	107	4		4
38	388	15046	107	4	4	4	3

Please help detect where is the error and how can resolve it. I really appreciate that. Thank you a lot.
ps: Nick: May I tag you here, sorry if any inconvenience cause you

Regards
Linh

[Nick Cox]

No error here. encode doesn't look inside the strings it encodes to see if there is a number present. It is sufficient that the value label carries the information.

If all your string values are numbers, you should be reaching for destring, not encode.

NB: your tag was not sufficient to reach me. In general, it is not an especially good idea to tag individuals unless you are quoting their posts.

[William Lisowski]

Adding a footnote to Nick's advice, when problems arise with a command a good place to start is with the online help for that command. In this example, type help encode into Stata's Command window and review the output. In that output you will find

Do not use encode if varname contains numbers that merely happen to be stored as strings; instead, use generate newvar = real(varname) or destring

[Marcos Almeida]

Also, if you really wish a given number for each category,
you can fiddle with - encode - plus the option - label - like in the toy example below.

. sysuseauto
command sysuseauto is unrecognized
r(199);

. sysuse auto
(1978 Automobile Data)

. codebook foreign

----------------------------------------------------------------------------------------------------------
foreign                                                                                           Car type
----------------------------------------------------------------------------------------------------------

                  type:  numeric (byte)
                 label:  origin

                 range:  [0,1]                        units:  1
         unique values:  2                        missing .:  0/74

            tabulation:  Freq.   Numeric  Label
                            52         0  Domestic
                            22         1  Foreign

. decode foreign, gen(for2)

. codebook for2

----------------------------------------------------------------------------------------------------------
for2                                                                                              Car type
----------------------------------------------------------------------------------------------------------

                  type:  string (str8)

         unique values:  2                        missing "":  0/74

            tabulation:  Freq.  Value
                            52  "Domestic"
                            22  "Foreign"

. label define mylab 11 "Foreign" 33 "Domestic"

. encode for2, gen(for3) label(mylab)

. codebook for3

----------------------------------------------------------------------------------------------------------
for3                                                                                              Car type
----------------------------------------------------------------------------------------------------------

                  type:  numeric (long)
                 label:  mylab

                 range:  [11,33]                      units:  1
         unique values:  2                        missing .:  0/74

            tabulation:  Freq.   Numeric  Label
                            22        11  Foreign
                            52        33  Domestic

Hopefully that helps.

[Linh mt]

Hi Nick, William and Marcos,

Thank you for your reply. The value of varname string reachange3 include both numeric and text as example below:

province	distric	commune	hoso	reachange2	reachange3	lydochange2	lydochange3
38	388	15046	107
38	388	15046	107
38	388	15046	107	4	4	4	4
38	388	15046	107	4		4
38	388	15046	107	4	4	4	3
38	388	15046	107	change job	move house	5	5
38	388	15046	107	suitable	move house	6	5
38	388	15046	107	change job	retired	5	6

However, I found where the mistake is. The reason is: reachange3 contains non-continuous numeric values, say 1,2,4,... Therefore, when encode reachange3, the numeric values 4 will be converted to 3.

@To William,
I think in this case, the destring command does not work, doesn't it because the varname include both numeric and text values?


Thank you very much all
Regards
Linh

[Marcos Almeida]

With regards to - destring -, if you type - help destring - in the command window, you'll find this information:

destring converts variables in varlist from string to numeric. If varlist
is not specified, destring will attempt to convert all variables in the
dataset from string to numeric. Characters listed in ignore() are
removed. Variables in varlist that are already numeric will not be
changed.
[...]
Either generate() or replace must be specified. With either option, if
any string variable contains nonnumeric characters not specified with
ignore(), then no corresponding variable will be generated, nor will that
variable be replaced (unless force is specified).

If I understood right, what you (wrongly) assumed as an error under - encode - command was the finding of different numbers (in 2 string variables) for the same level.

The way to assure these strings will represent the same code in both (encoded) variables is shown in #4.

No matter the absence of a few levels in one variable, or in the other variable, you can this way guarantee that, say, "4" means the same thing in both variables.

[Linh mt]

With regards to - destring -, if you type - help destring - in the command window, you'll find this information:




If I understood right, what you (wrongly) assumed as an error under - encode - command was the finding of different numbers (in 2 string variables) for the same level.

The way to assure these strings will represent the same code in both (encoded) variables is shown in #4.

No matter the absence of a few levels in one variable, or in the other variable, you can this way guarantee that, say, "4" means the same thing in both variables.

Hi @Marcos Almeida,

Thank you for reply. Actually, no problem with the encode. What I want to emphasize here is that I want to get the same values of string variable before and after ENDCODE. If the string var misses some levels, so the new var after ENCODE will miss some corresponding values. Say: the string var is below
reachange3
1
2
4
yes

After ENCODE, the newvar is numeric:
newvar
1
2
4
yes

but the actual values of newvar is
1
2
3
4

Hopefully my problem is clearly expressed. Now it is solved alreadly. Thank you again for helping me understand more about ENDCODE

Kind regards
linh

[Marcos Almeida]

As underlined in #6, the way to assure these strings will represent the same code in both (encoded) variables is shown in #4.

[Linh mt]

Yes, I got it. Thank you so much, Marcos
Best regards
Linh