How do I replace some elements of my list? {{a,b},{c,d}} ->{{1,b},{2,d}}

Questions
1

Hi,
I want replace some elements of my list “res” .

res = {{{a,b},{c,d},{e,f}}}

lis ={{1,2,3}}

I 'd like obtein :

rep = {{{1,b},{2,d},{3,f}}}

How to do with the command ReplacePart?

Thanks a lot

2

Hi,

here is a solution with ReplaceAll

ReplaceAll[res, MapThread[Rule, {res[[1, All, 1]], lis[[1]]}]]

and here is one without Replace at all:

Transpose[{lis[[1]], res[[1, All, 2]]}]

Cheers,
Marco

PS: Do you really need ReplacePart?

3

Hi,
very good reponse.
You are right, I haven’t need use “ReplacePart”.

I notice that you have practice with Mapthread. So, I could ask you another question.
If I use MapThread for Select, where is the position of select condition (I 'd like create a list where the elements are <=2) ?
for exemple
If I have this:

“res1= {1,2,3}” the command will be “Lat = Select[ res1 , #<=2. &];”

but with
res= {{1,2,3},{1,2,3},{1,4,5}}
. Which is the command
to have:

Lat = {{1,2},{1,2},{1,}}

MapThread[Select, res] (where is the position for the select condition?)

Thank you.

Margherita

4

Again, I am not sure whether you want MapThread here. You could try Map:

Map[Select[#, # <= 2 &] &, res]

or the short hand notation for that same thing:

Select[#, # <= 2 &] & /@ res

Cheers,

Marco

5

Thank you a lot.
Cheers,
Margherita

6

Hi Marco,
I have applied your suggestions in my problems. I have another questions for a similar cas "
ReplaceAll[res, MapThread[Rule, {res[[1, All, 1]], lis[[1]]}]]".

I have GG1 = {{0.220067, 0.440134, 0.634358, 0.828582, 1.}, {0.220067, 0.440134, 0.634358, 0.828582, 1.}}

res = {{{0.117779, 0.406482}, {0.235558, 0.333125}, {0.339506, 0.464985}, {0.443454, 0.544808}, {0.535196, 0.61788}},
{{0.117779, 0.406482}, {0.235558, 0.333125}, {0.339506, 0.464985}, {0.443454, 0.544808}, {0.535196, 0.61788}}}

If I do :

ReplaceAll[res, MapThread[Rule, {result[[All, All, 1]], GG1 }]]
it doesn’t run. Why?
result[[All, All, 1]] and GG1 have the same dimensions. The problem occurs because res has too many parenthesis?

Thank you

Cheers,
Margherita