如何在for循环中声明变量? (IDL) [英] How to declare variables in for loop? (IDL)

问题描述

例如，

我的文件在 00.dat，01.dat，02.dat ...之后命名，每个文件包含多列，我使用READCOL将它们读入变量.

My files are naming after 00.dat, 01.dat, 02.dat..., each file contains multiple columns and I use READCOL to read them into variables.

for i = 0, n-1 do begin
    readcol, string(i, F='(I02)')+'.dat', F='D,D', a0, b0
    readcol, string(i, F='(I02)')+'.dat', F='D,D', a1, b1
    .
    .
    c1 = a1 / a0
    c2 = a2 / a0
    .
    .
    d1 = b1 / b0
    d2 = b2 / b0
    .
    .
endfor

这很好用，但是如果有100个变量，我不能一一键入所有的varialbes.

This works fine, but I cannot type all the varialbes one by one if there will be, say, one hundred variables.

因此，我想使用for循环生成: a(i)，b(i)，c(i)，d(i).从这种意义上讲，代码将如下所示:

Therefore, I want to use for loop to generate: a(i), b(i), c(i), d(i). In that sense, the code will look like:

for i = 0, n-1 do begin
    readcol, string(i, F='(I02)')+'.dat',F='D,D', a(i), b(i)
endfor

for i = 0, n-1 do begin
    c(i) = a(i) / a(0)
    d(i) = b(i) / b(0)
endfor

但这是行不通的，有什么方法可以在for循环中以及在做数学时声明变量吗?

But this doesn't work, is there any method to declare variables in a for loop and while doing math?

(我不是英语母语人士.如果我的问题中有任何不清楚之处，请告诉我.谢谢！)

推荐答案

很高兴在StackOverflow上看到另一个IDL程序员！

Nice to see another IDL programmer on StackOverflow!

我认为部分问题是READCOL期望使用简单的变量名 它的输出，在第二个示例中，您给它数组表达式，例如 a(i)和b(i)而不是a和b.

I think part of the problem is that READCOL is expecting simple variable names for its outputs, and in your second example you're giving it array expressions like a(i) and b(i) instead of a and b.

如果我正确理解了您的问题，则想替换一维数组 第一个示例中的a0，a1，b0，b1等，带有二维数组a，b， 等等，其中每个数组都有维度(nfiles，samples_per_file).所以如果你知道 预先从每个文件读取多少行，您可以执行以下操作:

If I understand your question correctly, you want to replace the 1-dimensional arrays a0, a1, b0, b1, etc. from your first example, with 2-dimensional arrays a, b, etc. where each array has dimensions (nfiles, samples_per_file). So if you know in advance how many lines will be read from each file, you could do something like this:

a=dblarr(n,samples_per_file)
b=dblarr(n,samples_per_file)
; similarly for c, d, etc.

for i = 0, n-1 do begin
    readcol, string(i, F='(I02)')+'.dat',F='D,D', x, y
    a[i,*] = x
    b[i,*] = y
    c[i,*] = x/x[0]
    d[i,*] = y/y[0]
endfor

此版本传递READCOL所需的简单变量名称，然后将其复制 放入二维变量的子数组中.

This version passes READCOL the simple variable names it's expecting, then copies them into subarrays of the 2-D variables.

如果您事先不知道每个文件中有多少个样本，则可以分配 第一次循环迭代期间的二维数组:

If you don't know in advance how many samples are in each file, you could allocate the 2-d arrays during the first loop iteration:

for i = 0, n-1 do begin
    readcol, string(i, F='(I02)')+'.dat',F='D,D', x, y
    if (i EQ 0) then begin
       samples_per_file = n_elements(x)
       a = dblarr(n, samples_per_file)
       b = dblarr(n, samples_per_file)
       c = dblarr(n, samples_per_file)
       d = dblarr(n, samples_per_file)
    endif
    a[i,*] = x
    b[i,*] = y
    c[i,*] = x/x[0]
    d[i,*] = y/y[0]
endfor

当然，这全部假设每个文件包含相同数量的样本.如果不， 您可能需要将a，b，c和d更改为一维指针数组， 然后在读取文件时使用PTR_NEW为每个文件的数据分配内存.

Of course, this all assumes that each file contains the same number of samples. If not, you'd probably need to change a, b, c, and d to 1-dimensional arrays of pointers, then use PTR_NEW to allocate memory for each file's data as you read it.

(请注意，我使用方括号[]表示法进行数组索引，发现 比a(i)，b(i)等更容易阅读，后者可能与函数调用混淆.)

(Note that I've used the square bracket [] notation for array indexing, which I find a bit easier to read than a(i), b(i) etc. which can be confused with function calls.)

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