Tip: Import 3D Model

For whatever reason, some 3D models have to be imported in Mathematica.
The 3D model is stored as OBJ file. When it is imported, it loses the texture information.

(* set the color *)
roof = Import["greenroof.obj"]
roof = roof /. {l_Line :> {Thick,Black, l}, p_Polygon :> {FaceForm[Darker[Green]], p}}

Here the whole model:

Tip: Mathematica version of Maltab "Find" Function

I must say that if you work with Matlab everyday, it is really frustrated with Mathematica in some points.

Find is one of the most frequently used functions in Matlab.
Find(array>5.0): returns indices of the elements that are greater than 5.0.

In Mathematica, the corresponding function is Position

Position[array, #>5.0&] or Position[array, _>5.0] just doesn't work.

We "simple-minded" Matlab user have seldom thought about putting constraints on patterns

Then, this will do the job

Position[array, x : _ /; x > 5.0]

Position[array, x:_ /; testfunc[x]] will do better.

Tip: ListPlot3D and InterpolationOrder

Not exactly a tip.

10,000 random points
Regular grid: data = Table[RandomReal[], {100}, {100}];
Irregular grid: data = RandomReal[1, {10000, 3}];

Table[ListPlot3D[data, InterpolationOrder -> n, Mesh -> None]; // Timing, {n, {0, 1, 2, 3, 4}}]

Result (in seconds):
Interplotion Order: 0, 1, 2, 3, 4
Regular Gird: 0.771, 3.415, 3.435, 3.525, 3.565
Irregular Grid:6.349, 4.871, 4.767, 4.777, 4.737

Difference in zero-order interpolation is huge.

Reference: InterpolationOrder

Tip: Counting Files by Date

We like to know the number of the certain special type file processed month by month.
The following code will do the job:

(* all the files under one base direcotry *)
SetDirectory[basedirectory]
(* find all the files in all the subdirectories*)
files = FileNames["*.byt", {"*"}, Infinity];
(* return {year, month} for each file *)
data = Take[FileDate[basedirectory <> "\\" <> #], 2] & /@ files;
(* sort then count *)
cs = Tally[Sort[data]];
(* draw the graph *)
DateListPlot[cs, Filling -> Bottom, FillingStyle -> Blue, PlotStyle -> {Red, PointSize[Large]}, PlotRange -> {{{2006, 1}, {2008, 2}}, Automatic}, DateTicksFormat -> {"MonthShort", "/", "YearShort"}]

Fun with Map: Simple Geocoding with Yahoo Map API

Yahoo Map API has a simple REST interface which works well with Mathematica.
Here is an example to show a simple Geocoding function.

Problem: Give an address, return (longitude, latitude)

The basic query format:
http://local.yahooapis.com/MapsService/V1/geocode?appid=YahooDemo
&street=?&city=?&state=?


Let's try it with the address of Wolfram Research Inc.

geocoding[{"100 Trade Center Drive", "Champaign", "IL"}]
{-88.244868, 40.097855}

Is the result right? Let's check it out with Map Image API.


image[geocoding[{"100 Trade Center Drive", "Champaign", "IL"}]]



Notice:
1. I use "YahooDemo" as AppID, if you want to use this function frequently, please apply your own ID, it is free.
2. The Geocoding API is limited to 5, 000 queries per IP per day, Google Map has the similar limitation, so if you need geocoding a large amount of addresses, please use offline geocoding application.

reference: Yahoo Map API, Map Image API, Geocoding API

update:
Google version: see 1th comment , Thanks very much.