数组

数组

• REFORM 数组变形

将数组变为制定的维数

 A=indgen(20), B=reform(A,2,10) 

reform在默认（无输入参数）的情况下将数组变为一维

 A＝reform(data[1,*])

• 中位值

a=median(A,/even);偶数位的数据，取中间两个数的平均值

• rotate

可以把数组旋转后组成矩阵，类似于列操作。

a=indgen(10)
b=indgen(10)
c=[rotate(a,1),rotate(b,10]

转置

IDL>print,transpose([a,b])

• reverse

数组反向

例：数组降序排列,结合sort（默认升序）

PRINT, 'Elements of A in descending order: ', A[REVERSE(SORT(A))]

• 扩维

fan程序(http://astro.berkeley.edu/~johnjohn/idl.html#FAN )

IDL>print,fan(indgen(3),2)
IDL>print,fan(indgen(3),2,/trans)

可以用rebin实现

IDL>print,rebin(indgen(3),3,2)

• 多维数组的位置

用array_indices

 array = RANDOMU(seed, 10, 10)  
 mx = MAX(array, location) 
 ind=array_indices(array,location)
 print, ind, array[ind[0],ind[1]], format = '(%"Value at [%d, %d] is %f")'  

 IDL prints:
 Value at [3, 6] is 0.973381 

数组的位数,

print,size(array) 

size 还可以用来确定变量的类型 Ctype=size(A,/type),

• 数组随机打乱（shuffle)

Arr_S=arr[sort(randomu(seed,N_elements(arr))]

• 数组去重

Arr=Arr[uniq(Arr,sort(arr))

• 数组求和

a=total(indgen(10),/cum)；输出为数组的累计分布

数组和矩阵运算

• For A # B, where A and B are vectors, IDL performs A # TRANSPOSE(B). In this case, C = A # B is a matrix with Cij = Ai Bj. Mathematically, this is equivalent to the outer product, usually denoted by A Å B.
• For A ## B, where A and B are vectors, IDL performs TRANSPOSE(A) ## B. In this case, C = A ## B is a matrix with Cij = Bi Aj.
• To compute the dot product, usually denoted by A • B, use TRANSPOSE(A) # B.
• A # B = B ## A
• A # B = (BT # AT)T ;T表示转置运算